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

                                 April 14, 2005
                             ----------------------
                Date of Report (Date of earliest event reported)

                            OSI PHARMACEUTICALS, INC.
                            -------------------------
             (Exact name of registrant as specified in its charter)

           DELAWARE                    0-15190             13-3159796
           --------                   --------             -----------
(State or other jurisdiction of      (Commission        (I.R.S. Employer
        incorporation)               File Number)      Identification No.)

                              58 SOUTH SERVICE ROAD
                               MELVILLE, NY 11747
                    (Address of principal executive offices)

                                 (631) 962-2000
                                 --------------
              (Registrant's telephone number, including area code)

                                      N/A
                                 -------------
                        (Former name or former address,
                         if changed since last report.)

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:

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

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

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

[ ]   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 April 14, 2005, OSI Pharmaceuticals, Inc. ("OSI") purchased all of the
outstanding shares held by the minority shareholders of its then majority-owned
subsidiary, Prosidion Limited ("Prosidion"), resulting in Prosidion becoming a
wholly-owned subsidiary of OSI (the "Transaction"). Pursuant to the Transaction,
OSI entered into a Share Purchase Deed Relating to Shares of Prosidion Limited
(the "Share Purchase Deed") and an Amended and Restated Stock Incentive Plan
Stock Award Agreement (the "Stock Award Agreement") with Dr. Daryl Granner, a
member of the Board of Directors of OSI and a member of the Board of Directors
of Prosidion. In connection with the Transaction, OSI agreed to pay Dr. Granner
$176,000 in cash for his 11,000 ordinary shares of Prosidion, as provided in the
Share Purchase Deed, which is attached hereto as Exhibit 10.1 and incorporated
herein by reference. In addition, Dr. Granner agreed to exchange his rights to
2,000 ordinary shares of Prosidion for 592 shares of OSI common stock in
consideration for his continued service as a member of Prosidion's Scientific
Advisory Board (the "SAB"), as provided in the Stock Award Agreement, which is
attached hereto as Exhibit 10.2 and incorporated herein by reference. Pursuant
to the Stock Award Agreement, Dr. Granner will be issued 296 shares of OSI's
common stock on October 1, 2005 and the remaining shares on October 1, 2006
provided that Dr. Granner's service as a member of the SAB has not terminated
for any reason prior to each such date.

ITEM 9.01 EXHIBITS



EXHIBIT NO.                             DESCRIPTION
- ----------                              -----------
             
   10.1         Share Purchase Deed Relating to Shares of Prosidion Limited,
                dated April 14, 2005, between OSI Pharmaceuticals, Inc. and Dr. Daryl Granner.

   10.2         Amended and Restated Stock Incentive Plan Stock Award Agreement, dated April 14,
                2005, between OSI Pharmaceuticals, Inc. and Dr. Daryl Granner.


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                                    SIGNATURE

      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 hereunto duly authorized.

      Date: April 20, 2005           OSI PHARMACEUTICALS, INC.

                                     By: /s/ Robert L. Van Nostrand
                                         ------------------------------------
                                         Robert L. Van Nostrand
                                         Vice President and Chief Financial
                                         Officer (Principal Financial Officer)

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                                  EXHIBIT INDEX


EXHIBIT NO.                          DESCRIPTION
- ----------                           -----------
             
  10.1          Share Purchase Deed Relating to Shares of Prosidion Limited,
                dated April 14, 2005, between OSI Pharmaceuticals, Inc. and
                Dr. Daryl Granner.

  10.2          Amended and Restated Stock Incentive Plan Stock Award Agreement,
                dated April 14, 2005, between OSI Pharmaceuticals, Inc. and
                Dr. Daryl Granner.


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