On May 5, 2008, Senior Housing Properties Trust, or we, entered into a series of Purchase and Sale Agreements, or the Purchase Agreements, with HRPT Properties Trust, or HRPT, and certain of its subsidiaries for the purchase of 48 medical office, clinic and biotech laboratory buildings (containing approximately 2.2 million square feet in the aggregate) for purchase prices aggregating $565 million. The properties that we plan to acquire are currently 98.3% leased to approximately 370 unaffiliated tenants for an average term of 6.7 years.

Under the individual Purchase Agreements, we have agreed to pay aggregate purchase prices of approximately $554 million in cash and to assume three mortgages on two properties which total approximately $11 million. The terms of the mortgages permit prepayment at various times; some of those debt prepayments may require premiums according to contractual formulas. We intend to fund the proposed purchases with cash on hand, borrowings under our revolving credit facility and by assuming the three mortgages. We expect to eventually fund the proposed purchases with a combination of long term capital determined based upon market conditions. For purposes of Item 9.01 of this report, we have assumed that we will incur approximately $150 million of additional mortgage debt to fund the proposed purchases.

The transactions under the individual Purchase Agreements are scheduled to close in phases over the next 12 months, and the timings of the closings may be accelerated in certain circumstances. The transactions are subject to various closing conditions and contingencies typical of large commercial real estate transactions, including, among other matters, waiver of any rights of first refusal held by tenants, the consent of mortgagees to the sales of the buildings which are encumbered by mortgages and financing contingencies relating to certain properties which have an aggregate purchase price of approximately $245 million. As a result, some or all of these properties may not be purchased.

We were formerly a 100% owned subsidiary of HRPT. We were spun off to HRPT shareholders in 1999 and, at the time of this spin off, we and HRPT entered into a Transaction Agreement which, among other things, prohibited us from purchasing medical office, clinic and biotech laboratory buildings. Concurrently with the execution and delivery of the Purchase Agreements, we and HRPT entered into an amendment to the Transaction Agreement, or the First Amendment Agreement, to permit us, rather than HRPT, to invest in medical office, clinic and biomedical, pharmaceutical and laboratory buildings, whether of single purpose or mixed use.
The First Amendment Agreement is subject, in the case of mixed use buildings, to HRPT retaining the right to invest in any mixed use building for which the rentable square footage is less than 50% medical office, clinic and biomedical, pharmaceutical and laboratory use.

Concurrently with the execution and delivery of the Purchase Agreements and the First Amendment Agreement, we and HRPT also entered into a Right of First Refusal Agreement pursuant to which we acquired a right of first refusal to purchase up to 45 identified additional properties (approximately 4.6 million square feet) that are currently leased by HRPT principally to tenants in medical related businesses, in the event that HRPT determines to sell such properties or in the event of a change of control of HRPT or of the subsidiary which owns such properties.

We and HRPT are managed by Reit Management & Research LLC, or RMR, which is beneficially owned by Messrs. Barry M. Portnoy and Adam D. Portnoy. In addition, Messrs. Barry M. Portnoy, Frederick N. Zeytoonjian and Adam D. Portnoy, three of our current trustees, also serve as trustees of HRPT, and we own 1,000,000 of HRPT's common shares. The sale prices for the properties to be sold were established by reference to an independent appraisal and the terms of the transactions were negotiated by special committees of each company's board of trustees comprised solely of independent trustees.

We expect to enter into a new property management agreement with RMR with respect to the buildings we acquire from HRPT. The current property management agreement between HRPT and RMR with respect to these buildings provides, in general, for property management fees equal to 3% of gross rents and construction management fees equal to 5% of certain construction costs, as well as reimbursement of certain administrative costs. We also expect to amend our existing advisory agreement with RMR in connection with these acquisitions. Under the current advisory agreement, the management fees payable by us to RMR are principally based on our historical cost of our properties. We expect the amendment will provide that the management fees with respect to any of the 48 properties which we acquire from HRPT will be based on HRPT's historical costs rather than our higher purchase prices, so that the fees paid to RMR will equal the fees that are currently being paid by HRPT with respect to these properties. RMR will not receive any additional compensation or fees in relation to these acquisitions.

The descriptions of the Purchase Agreements, the First Amendment Agreement and the Right of First Refusal Agreement are qualified in their entirety by reference to the Purchase Agreements, the First Amendment Agreement and the Right of First Refusal Agreement, which are filed as Exhibits 10.1 to 10.23 to this Current Report on Form 8-K and incorporated herein by reference.

THIS FORM 8-K CONTAINS FORWARD LOOKING STATEMENTS WITHIN THE MEANING OF THE PRIVATE SECURITIES LITIGATION REFORM ACT OF 1995 AND OTHER FEDERAL SECURITIES LAWS. WHENEVER WE USE WORDS SUCH AS "BELIEVE", "EXPECT", "ANTICIPATE", "INTEND", "PLAN", "ESTIMATE" OR SIMILAR EXPRESSIONS, WE ARE MAKING FORWARD LOOKING STATEMENTS. THESE FORWARD LOOKING STATEMENTS ARE BASED UPON OUR PRESENT INTENT, BELIEFS OR EXPECTATIONS, BUT FORWARD LOOKING STATEMENTS ARE NOT GUARANTEED TO OCCUR AND MAY NOT OCCUR. ACTUAL RESULTS MAY DIFFER MATERIALLY FROM THOSE CONTAINED IN OR IMPLIED BY OUR FORWARD LOOKING STATEMENTS AS A RESULT OF VARIOUS FACTORS.

FOR EXAMPLE, THIS FORM 8-K STATES THAT WE HAVE AGREED TO PURCHASE 48 MEDICAL OFFICE, CLINIC AND BIOTECH LABORATORY BUILDINGS FOR $565 MILLION AND THAT THESE SALES ARE EXPECTED TO BE COMPLETED DURING THE NEXT 12 MONTHS. IN FACT, OUR OBLIGATION TO COMPLETE THESE PURCHASES IS SUBJECT TO VARIOUS CONDITIONS TYPICAL OF LARGE COMMERCIAL REAL ESTATE PURCHASES, INCLUDING, WITH RESPECT TO CERTAIN PROPERTIES,

OBTAINING CONSENTS FROM MORTGAGEES AND WAIVERS OF RIGHTS OF FIRST REFUSAL FROM TENANTS. ALSO, WE HAVE FINANCING CONTINGENCIES RELATING TO CERTAIN PROPERTIES FOR AN AGGREGATE PURCHASE PRICE OF APPROXIMATELY $245 MILLION. AS A RESULT OF ANY FAILURE OF THESE CONDITIONS, SOME PROPERTIES MAY NOT BE PURCHASED, THE PURCHASE PRICES PAYABLE BY US MAY BE CHANGED OR SOME OF THESE PURCHASES MAY BE ACCELERATED OR DELAYED.

OTHER IMPORTANT FACTORS THAT COULD CAUSE ACTUAL RESULTS TO DIFFER MATERIALLY FROM THOSE IN FORWARD LOOKING STATEMENTS ARE DESCRIBED MORE FULLY UNDER "ITEM 1A. RISK FACTORS" IN OUR ANNUAL REPORT ON FORM 10-K FOR THE YEAR ENDED DECEMBER 31, 2007.

YOU SHOULD NOT PLACE UNDUE RELIANCE UPON FORWARD LOOKING STATEMENTS.

EXCEPT AS REQUIRED BY LAW, WE UNDERTAKE NO OBLIGATION TO UPDATE OR REVISE ANY FORWARD LOOKING STATEMENTS AS A RESULT OF NEW INFORMATION, FUTURE EVENTS OR OTHERWISE.

Pursuant to the requirements of Rule 3-14 of Regulation S-X, this Current Report on Form 8-K includes (i) a Combined Statement of Revenues and Certain Operating Expenses for six medical properties proposed to be acquired from HRPT, collectively referred to as HRPT Medical Properties, for the three months ended March 31, 2008 and 2007 (unaudited) and for the years ended December 31, 2007, 2006, and 2005, and (ii) pro forma financial data for us, which includes the 48 medical office, clinic and biotech laboratory buildings proposed to be acquired from HRPT as well as other acquisitions we have completed since January 1, 2008 (balance sheet) and January 1, 2007 (statements of income). Because changes will likely occur in occupancy, rents and expenses with respect to the properties to be acquired and because some or all of the acquisitions may not be completed, the historical financial statements and pro forma financial data presented should not be considered as a projection of future results. Differences could also result from, among other considerations, changes in our portfolio of investments, in interest rates and in our capital structure.

Between January 1, 2008 and April 30, 2008, we acquired the following additional senior living properties (dollars in thousands):

  Date                  Number of             Purchase
Acquired    Location    Properties   Units   Price (1)
 1/1/08        WI                5     568   $   66,767
 2/7/08        TX                2      98       10,292
2/17/08        NE                1     138        9,338
 3/1/08        MN                1     228       48,549
3/31/08    CA, DE, MD           10     660      137,445
                                19   1,692   $  272,391

We funded these acquisitions using cash on hand, proceeds from equity issuances and borrowings under our revolving credit facility.

(a) Financial Statements of Businesses Acquired.

Combined Statements of Revenues and Certain Operating Expenses for HRPT Medical
Properties.



Report of Independent Registered Public Accounting Firm                       F-1
Combined Statements of Revenues and Certain Operating Expenses for the
Three Months Ended March 31, 2008 and 2007 (unaudited), and for the
Years Ended December 31, 2007, 2006 and 2005                                  F-2

The historical financial statements listed in Item 9.01(a) present the results of operations of the HRPT properties during periods prior to their expected acquisition by

us and exclude, as permitted by Rule 3-14 of Regulation S-X, items of revenue and expense which are not comparable to the expected future operations by us.

(b) Pro Forma Financial Information.

Introduction to Unaudited Pro Forma Condensed Consolidated Financial Statements F-5 Unaudited Pro Forma Condensed Consolidated Balance Sheet as of March 31, 2008 F-7 Unaudited Pro Forma Condensed Consolidated Statement of Income for the Three Months Ended March 31, 2008 F-8 Unaudited Pro Forma Condensed Consolidated Statement of Income for the Year Ended December 31, 2007 F-9 Notes to Unaudited Pro Forma Condensed Consolidated Financial Statements F-10

(d) Exhibits.

10.1     Purchase and Sale Agreement, dated as of May 5, 2008, among HRPT
         Properties Trust, HUB Properties Trust and MOB Realty Trust, as Sellers,
         and Senior Housing Properties Trust, as Purchaser (with respect to 21
         properties located in Massachusetts, Pennsylvania, and New York).

10.2     Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to Torrey Pines, 3030-50, Science Park Road, San
         Diego, California).

10.3     Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to Amelia Building, 855 Kempsville Road,
         Norfolk, Virginia).

10.4     Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to Halifax Building, 6161 Kempsville Circle,
         Norfolk, Virginia).

10.5     Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to Fair Oaks, 4001 Fair Ridge Drive, Fairfax,
         Virginia).

10.6     Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to 2141 K Street, NW, Washington, DC).

10.7     Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to 6818 Austin Center Blvd., Austin, Texas).

10.8     Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to 1145 19th Street, NW, Washington, DC).

10.9     Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to Oklahoma Clinics, 8315 So. Walker Ave., 701
         NE 10th Street, 200 N. Bryant, 600 National Ave., Oklahoma City,
         Oklahoma).

10.10    Purchase and Sale Agreement, dated as of May 5, 2008, between HRPT
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to HIP of White Plains, 15 North Broadway, White
         Plains, New York).

10.11    Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to 4770 Regent Boulevard, Irving, Texas).

10.12    Purchase and Sale Agreement, dated as of May 5, 2008, between HUB RI
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to 701 George Washington Highway, Lincoln, Rhode
         Island).

10.13    Purchase and Sale Agreement, dated as of May 5, 2008, between 4 Maguire
         Road Realty Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to 4 Maguire Road, Lexington, Massachusetts).

10.14    Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to 4000 Old Court Road, Pikesville, Maryland).

10.15    Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to 1825, 1911 and 1925 N. Mills Avenue, Orlando,
         Florida).

10.16    Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to Bailey Square, 1111 W. 34th Street, Austin,
         Texas).

10.17    Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to Brittonfield II and III, Lot 5E-2 and Lot
         5E-1, 5008 Brittonfield Parkway, East Syracuse, New York).

10.18    Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to Centre Commons, 5750 Centre Ave., Pittsburgh,
         Pennsylvania).

10.19    Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to 710 North Euclid, Anaheim, California).

10.20    Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Properties Trust, as Seller, and Senior Housing Properties Trust, as
         Purchaser (with respect to 525 Virginia Drive, Fort Washington,
         Pennsylvania).

10.21    Purchase and Sale Agreement, dated as of May 5, 2008, between HUB
         Northeast Medical Arts Center LLC, as Seller, and Senior Housing
         Properties Trust, as Purchaser (with respect to Northeast Medical Arts
         Center, 2801 North Decatur Road, Decatur, Georgia).

10.22    Right of First Refusal Agreement dated as of May 5, 2008 between HRPT
         Properties Trust, Blue Dog Properties Trust, Cedars LA LLC, HRP NOM
         L.P., HRP NOM 2 L.P., HRPT Medical Buildings Realty Trust, HUB
         Properties Trust, Lakewood Property Trust, LTMAC Properties LLC, HUB
         Mid-West LLC, and Rosedale Properties Limited Liability Company, as
         Grantors, and Senior Housing Properties Trust.

10.23    First Amendment to Transaction Agreement, dated as of May 5, 2008,
         between Senior Housing Properties Trust and HRPT Properties Trust.

23.1     Consent of Ernst & Young LLP.

To the Board of Trustees of Senior Housing Properties Trust

We have audited the accompanying combined statements of revenues and certain operating expenses of HRPT Medical Properties, for each of the three years ended December 31, 2007. These statements are the responsibility of HRPT Medical Properties' management. Our responsibility is to express an opinion on the statements based on our audits.

We conducted our audits in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the statements. An audit also includes assessing the basis of accounting used and significant estimates made by management, as well as evaluating the overall statements presentation. We believe that our audits provide a reasonable basis for our opinion.

The accompanying statements were prepared for the purpose of complying with the rules and regulations of the Securities and Exchange Commission for inclusion in the Current Report on Form 8-K of Senior Housing Properties Trust, as described in Note 1, and are not intended to be a complete presentation of HRPT Medical Properties' revenues and expenses.

In our opinion, the statements referred to above present fairly, in all material respects, the combined revenues and certain operating expenses described in Note 1 of HRPT Medical Properties for each of the three years ended December 31, 2007, in conformity with U.S. generally accepted accounting principles.

Boston, Massachusetts

May 7, 2008

                            HRPT Medical Properties



         COMBINED STATEMENTS OF REVENUES AND CERTAIN OPERATING EXPENSES



                                 Three Months Ended
                                     March 31,                       Year Ended December 31,
                                2008           2007            2007            2006            2005
                                    (unaudited)
REVENUES:
Rental income                $ 3,267,456    $ 3,251,492    $ 13,033,578    $ 12,214,358    $ 11,542,973
Reimbursement from
tenants and other income         691,909        876,563       3,336,652       2,980,214       3,987,216
                               3,959,365      4,128,055      16,370,230      15,194,572      15,530,189

CERTAIN OPERATING
EXPENSES:
Property operating
expenses                         513,020        481,739       2,101,373       2,164,588       2,955,395
Real estate taxes and
insurance                        422,008        371,262       1,697,752       1,555,850       1,475,077
                                 935,028        853,001       3,799,125       3,720,438       4,430,472

REVENUES IN EXCESS OF
CERTAIN OPERATING
EXPENSES $ 3,024,337 $ 3,275,054 $ 12,571,105 $ 11,474,134 $ 11,099,717

See accompanying notes.

1. General Information and Summary of Significant Accounting Policies

HRPT Properties Trust, a Maryland real estate investment trust, ("HRPT") owns and operates six medical office properties containing 389,149 square feet of space located in Austin, TX, Pittsburgh, PA and San Diego, CA (the "HRPT Medical Properties"). The HRPT Medical Properties are managed by Reit Management & Research, LLC, or RMR. On May 5, 2008, Senior Housing Properties Trust ("SNH") agreed to acquire the HRPT Medical Properties.

The accompanying combined financial statements have been prepared in accordance with Rule 3-14 of Regulation S-X of the Securities and Exchange Commission for inclusion in the Current Report on Form 8-K of SNH. Accordingly, certain historical expenses that may not be comparable to the expenses expected to be incurred in the future have been excluded. Excluded expenses consist of depreciation and amortization, interest expense and other costs not directly related to the future operations.

Use of Estimates. Preparation of financial statements in conformity with U.S. generally accepted accounting principles requires HRPT management to make estimates and assumptions that may affect the amounts reported in the financial statements and related notes. The actual results could differ from these estimates.

Revenue Recognition. Tenant leases are accounted for as operating leases. Rental income is recognized on a straight-line basis over the life of the lease agreements. Straight-line rent adjustments included in rental income on the combined statements of revenues and certain operating expenses totaled $919,449, $1,985,591 and $4,532,383, for the years ended December 31, 2007, 2006 and 2005, respectively.

Reimbursement from Tenants. Reimbursements from tenants, principally for increases in operating expenses and real estate taxes over base year amounts, are recognized when they become billable to the tenants.

2. Leases

HRPT, as lessor, has entered into non-cancelable operating leases at the HRPT Medical Properties. These leases will be assumed by SNH when the HRPT Medical Properties are acquired. Future minimum rentals under the leases in effect at December 31, 2007, are summarized as follows:

Year            Amount
2008         $  12,356,072
2009            12,405,759
2010            12,181,470
2011            11,781,627
2012            11,287,140
Thereafter      72,557,126
             $ 132,569,194

Leases are generally for terms greater than one year and for no more than 20 years and provide for operating expenses and real estate tax escalations and renewal options.

For the years ended December 31, 2007, 2006 and 2005, two tenants, The Scripps Research Institute and Columbia/HCA Healthcare Corporation, comprised 69%, 66% and 66% of rental income, respectively.

3. Related Person Transactions

HRPT paid certain fees to RMR in connection with its management of the HRPT Medical Properties, including property management fees equal to 3% of gross rents and construction management fees equal to 5% of certain construction costs. HRPT also reimbursed RMR for certain administrative services. Total fees and reimbursements paid to RMR by HRPT were $737,239, $688,791 and $621,560, for the years ended December 31, 2007, 2006 and 2005, respectively. Upon acquisition of the HRPT Medical Properties, the HRPT Medical Properties will continue to be managed by RMR under a similar arrangement with SNH.

Introduction to Unaudited Pro Forma Condensed Consolidated Financial Statements

The following unaudited pro forma condensed consolidated balance sheet as of March 31, 2008, reflects our financial position as if the transactions described in the footnotes to the unaudited pro forma condensed consolidated financial statements were completed on March 31, 2008. The unaudited pro forma condensed consolidated statements of income for the three months ended March 31, 2008, and the year ended December 31, 2007, present our results of operations as if the transactions described in the notes to the unaudited pro forma condensed consolidated financial statements were completed on January 1, 2007. These unaudited pro forma condensed consolidated financial statements should be read in connection with our financial statements for the three months ended March 31, 2008, included in our Quarterly Report on Form 10-Q, our financial statements for the year ended December 31, 2007, included in our Annual Report on Form 10-K, and the financial statements included in Item 9.01(a) of this Form 8-K.

The unaudited pro forma financial statements assume the acquisitions of 48 medical office, clinic and biotech laboratory buildings from HRPT Properties Trust, or HRPT, are financed with borrowings under our revolving credit facility, obtaining a mortgage for $150 million at 7.9% per annum and assuming three mortgage debts totaling $11 million on two of the properties. We expect to eventually fund these acquisitions with a mix of long term capital determined based upon market conditions. These unaudited pro forma financial statements are provided for information purposes only and upon completion of the planned long term financing for these acquisitions our financial position and results of our operations will be significantly different than what is presented in these unaudited pro forma financial statements. In the opinion of management, all . . .