UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT PURSUANT
TO SECTION 13 OR 15(d) OF THE
SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported): September 23, 2011 (September 20, 2011)

SENIOR HOUSING PROPERTIES TRUST

(Exact Name of Registrant as Specified in Its Charter)

Two Newton Place, 255 Washington Street, Suite 300, Newton, Massachusetts 02458-1634

(Address of Principal Executive Offices) (Zip Code)

617-796-8350

(Registrant’s Telephone Number, Including Area Code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

o            Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o            Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o            Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o            Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 1.01.  Entry into a Material Definitive Agreement.

On September 20, 2011, Senior Housing Properties Trust, or we, our or us, entered into a series of 13 agreements, or the Purchase Agreements, for the purchase of 13 properties which are majority leased as medical office buildings and to tenants in medical related businesses, or MOBs, for purchase prices aggregating $167 million, payable in cash.  The properties to be purchased include approximately 1.3 million square feet in the aggregate and are located in eight states. We intend to fund the proposed purchases using cash on hand and borrowings under our $750 million unsecured revolving credit facility.

The 13 properties we have agreed to purchase are currently 95% occupied on a combined basis and have a weighted (by rents) average remaining lease term of approximately 5.0 years.

The purchases under the individual Purchase Agreements are expected to be completed before year end 2011.  The purchases are subject to various closing conditions and contingencies typical of large commercial real estate transactions.  As a result, some or all of these purchases may be delayed or may not occur.

The descriptions of the Purchase Agreements are qualified in their entirety by reference to the Purchase Agreements, which are filed as Exhibits 10.1 to 10.13 to this Current Report and incorporated herein by reference.

The 13 properties are to be purchased from, and the other parties to the Purchase Agreements are, CommonWealth REIT, or CWH, and certain of its subsidiaries.  We were a 100% owned subsidiary of CWH until our common shares were spun off to CWH’s shareholders in 1999.  As a result of agreements entered into by us, CWH and others in connection with the spin off and subsequently, we acquired a right of first refusal to purchase from CWH and its subsidiaries certain properties (approximately 4.6 million square feet) leased by CWH principally to tenants in medical related businesses, including certain of the properties that are subject to the Purchase Agreements.  Upon the conclusion of the purchases under the individual Purchase Agreements, substantially all of the properties subject to our right of first refusal will have been purchased by us, and we and CWH have agreed to terminate the existing right of first refusal.

Reit Management & Research LLC, or RMR, provides management services to both us and CWH. One of our Managing Trustees, Barry M. Portnoy, is Chairman and majority owner of RMR.  Adam D. Portnoy, our other Managing Trustee, is Mr. Barry Portnoy’s son, and he beneficially owns the remainder of RMR and is a director and the President and Chief Executive Officer of RMR.  Messrs. Barry Portnoy and Adam Portnoy also serve as Managing Trustees of CWH, and Frederick N. Zeytoonjian serves as an Independent Trustee of us and of CWH.  Each of our and CWH’s executive officers are also officers of RMR.  Our Independent Trustees also serve as directors or trustees of other public companies to which RMR provides management services; Mr. Barry Portnoy serves as a managing director or trustee of those companies, and Mr. Adam Portnoy serves as a managing trustee of some of those companies.  We also own 250,000 common shares of CWH.  The terms of the purchases of the 13 properties were negotiated by special committees of each of our and CWH’s Boards of Trustees composed solely of independent trustees who are not also trustees of the other party, and we and CWH were represented by separate counsel.  Also, the purchase prices for the properties to be acquired were established by reference to an appraisal by a nationally recognized real estate appraisal firm.

We currently own approximately 14.29% of the outstanding equity of Affiliates Insurance Company, or AIC.  The other shareholders of AIC are RMR and five other companies to which RMR provides management services, including CWH.  All of our Trustees and all of the trustees and directors of the other publicly held AIC shareholders currently serve on the board of directors of AIC.  In 2010, AIC designed a combination property insurance program for us and other AIC shareholders in which AIC participated as a reinsurer.  That program was modified and extended in 2011.

For more information about the relationships among us, our Trustees and executive officers, RMR, CWH, AIC and other companies to which RMR provides management services, and about the risks which may arise from these relationships, please refer to our filings with the Securities and Exchange Commission, or the SEC, including our Annual Report on Form 10-K filed for the year ended December 31, 2010, or our Annual Report (including the sections captioned “Business,” “Risk Factors” (as such section was revised and updated in our Quarterly Report on Form 10-Q for the quarter ended June 30, 2011, or our Quarterly Report) and “Management’s Discussion and

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Analysis of Financial Condition and Results of Operations—Related Person Transactions”), our Quarterly Report (including the section captioned “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Related Person Transactions”) and our Proxy Statement dated February 24, 2011 relating to our 2011 Annual Shareholders Meeting, or our Proxy Statement (including the information regarding our Trustees and executive officers and the section captioned “Related Person Transactions and Company Review of Such Transactions”).  Our filings with the SEC, including our Annual Report, our Quarterly Report and our Proxy Statement, are available at the SEC’s website: www.sec.gov.

WARNING CONCERNING FORWARD LOOKING STATEMENTS

THIS CURRENT REPORT CONTAINS STATEMENTS WHICH CONSTITUTE FORWARD LOOKING STATEMENTS WITHIN THE MEANING OF THE PRIVATE SECURITIES LITIGATION REFORM ACT OF 1995 AND OTHER 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 AND THEIR IMPLICATIONS ARE BASED UPON OUR PRESENT INTENT, BELIEFS OR EXPECTATIONS, BUT FORWARD LOOKING STATEMENTS AND THEIR IMPLICATIONS ARE NOT GUARANTEED TO OCCUR AND MAY NOT OCCUR.  OUR ACTUAL RESULTS MAY DIFFER MATERIALLY FROM THOSE CONTAINED IN OR IMPLIED BY OUR FORWARD LOOKING STATEMENTS AS A RESULT OF VARIOUS FACTORS, INCLUDING SOME THAT ARE BEYOND OUR CONTROL.  FOR EXAMPLE:

·                                          THIS CURRENT REPORT STATES THAT WE HAVE AGREED TO PURCHASE 13 PROPERTIES FOR $167 MILLION AND THAT THESE PURCHASES ARE EXPECTED TO BE COMPLETED BEFORE YEAR END 2011.  OUR OBLIGATIONS TO COMPLETE THESE PURCHASES ARE SUBJECT TO VARIOUS CONDITIONS TYPICAL OF LARGE, COMMERCIAL REAL ESTATE TRANSACTIONS.  IN THE EVENT THESE CONDITIONS ARE NOT SATISFIED, SOME OF THESE PURCHASES MAY BE DELAYED OR MAY NOT OCCUR.

·                                          THIS CURRENT REPORT STATES THAT THE PURCHASE PRICES TO BE PAID BY US WERE ESTABLISHED BY REFERENCE TO AN APPRAISAL REPORT AND THAT THE PURCHASE TERMS WERE NEGOTIATED BY SPECIAL COMMITTEES OF INDEPENDENT TRUSTEES OF EACH OF US AND CWH REPRESENTED BY SEPARATE COUNSEL.  AN IMPLICATION OF THESE STATEMENTS MAY BE THAT THE PURCHASE PRICES AND OTHER TERMS OF THESE TRANSACTIONS ARE AS FAVORABLE TO US AS THOSE IN ARM’S LENGTH TRANSACTIONS.  WE AND CWH ARE BOTH MANAGED BY RMR AND HAVE COMMON TRUSTEES AND OTHER RELATIONSHIPS.  ACCORDINGLY, WE AND CWH MAY BE CONSIDERED TO BE RELATED PARTIES AND THERE CAN BE NO ASSURANCE THAT THE PURCHASE PRICES AND OTHER TERMS OF THE TRANSACTIONS ARE THE SAME OR AS FAVORABLE TO US AS WE WOULD HAVE OBTAINED ARM’S LENGTH TRANSACTIONS BETWEEN UNRELATED PARTIES.

THE INFORMATION CONTAINED IN OUR FILINGS WITH THE SEC, INCLUDING UNDER THE CAPTION “RISK FACTORS” IN OUR ANNUAL REPORT AND OUR QUARTERLY REPORT, OR INCORPORATED THEREIN, IDENTIFIES OTHER IMPORTANT FACTORS THAT COULD CAUSE ACTUAL RESULTS TO DIFFER MATERIALLY FROM THOSE IN OUR FORWARD LOOKING STATEMENTS.  OUR FILINGS WITH THE SEC ARE AVAILABLE AT THE SEC WEBSITE, WWW.SEC.GOV.

YOU SHOULD NOT PLACE UNDUE RELIANCE UPON OUR FORWARD LOOKING STATEMENTS.

EXCEPT AS REQUIRED BY LAW, WE DO NOT INTEND TO UPDATE OR CHANGE ANY FORWARD LOOKING STATEMENTS AS A RESULT OF NEW INFORMATION, FUTURE EVENTS OR OTHERWISE.

Item 8.01.  Other Events.

On September 21, 2011, we issued a press release announcing that we had entered the Purchase Agreements, which Purchase Agreements are further described in Item 1.01 of this Current Report.  A copy of that press release is filed as Exhibit 99.1 to this Current Report.

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Item 9.01.  Financial Statements and Exhibits.

(d)                                                         Exhibits.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

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