<PAGE>   1

      As filed with the Securities and Exchange Commission on July 26, 2000

                                                 Registration No. ______________

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      under
                           THE SECURITIES ACT OF 1933
                             -----------------------

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

<TABLE>
<CAPTION>
<S>                                                                 <C>
                                     Delaware                               13-3159796
                        ------------------------------              --------------------------
                       (State or other jurisdiction of                 (I.R.S. Employer
                        incorporation or organization)                Identification No.)

                          106 Charles Lindbergh Blvd.
                                 Uniondale, NY                                11553
                        ------------------------------              --------------------------
                    (Address of principal executive offices)               (Zip Code)
</TABLE>

                             -----------------------
                            OSI PHARMACEUTICALS, INC.
                         NON-QUALIFIED STOCK OPTION PLAN
                             FOR FORMER EMPLOYEES OF
                           CADUS PHARMACEUTICAL CORP.
                                       AND
                            OSI PHARMACEUTICALS, INC.
                               1999 INCENTIVE AND
                                  NON-QUALIFIED
                                STOCK OPTION PLAN
                            (Full title of the plan)
                             -----------------------
                             ROBERT L. VAN NOSTRAND
                   VICE PRESIDENT AND CHIEF FINANCIAL OFFICER
                            OSI PHARMACEUTICALS, INC.
                           106 CHARLES LINDBERGH BLVD.
                            UNIONDALE, NEW YORK 11553
                                 (516) 222-0023
            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)
                             -----------------------

                                    Copy to:

                         SPENCER W. FRANCK, JR., ESQUIRE
                         SAUL, EWING, REMICK & SAUL LLP
                               CENTRE SQUARE WEST
                         1500 MARKET STREET, 38TH FLOOR
                        PHILADELPHIA, PENNSYLVANIA 19102
                                 (215) 972-1955
                             -----------------------
               See next page for calculation of registration fee.
                             -----------------------


<PAGE>   2

                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
=====================================================================================================================
                                         Proposed Maximum   Proposed Maximum
 Title of Securities     Amount to be    Offering Price        Aggregate
   to be Registered       Registered        Per Share       Offering Price        Amount of Registration Fee (5)
---------------------------------------------------------------------------------------------------------------------
<S>                     <C>                  <C>           <C>                              <C>
Common Stock, Par         334,632(1)         $ 5.0000      $   1,673,160.00
Value $.01 Per Share       25,000(2)         $14.0000      $     350,000.00
                          742,125(3)         $23.2500      $  17,254,406.25
                        1,257,875(4)         $31.78125     $  39,976,839.84                  $15,643.16
                        ---------                             -------------                   =========
                        2,359,632                                  X.000264
                        =========                           ===============
=====================================================================================================================
</TABLE>

(1)      Represents shares issuable upon exercise of options previously granted
         under the Non-Qualified Stock Option Plan for Former Employees of Cadus
         Pharmaceutical Corp. (the "Cadus Plan").
(2)      Represents shares issuable upon exercise of options previously granted
         under the Cadus Plan.
(3)      Represents shares issuable upon exercise of options previously granted
         under the 1999 Incentive and Non-Qualified Stock Option Plan (the "1999
         Plan").
(4)      Represents shares issuable in connection with options available for
         grant under the 1999 Plan.
(5)      The registration fee has been computed in accordance with paragraphs
         (c) and (h) of Rule 457, based upon, in the case of options previously
         granted, the stated exercise price of such options, and, in the case of
         options still available for grant, the average of the reported high and
         low sale prices of shares of the Registrant's common stock on July 20,
         2000.

<PAGE>   3

                                  PART I

             INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

Item 1.        Plan Information.(1)

Item 2.        Registrant Information and Employee Plan Annual Information.(1)

                                  PART II

             INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.        Incorporation of Documents by Reference.

               The documents listed in clauses (a), (b) and (c) below are
incorporated herein by this reference thereto, and all documents subsequently
filed by the Registrant pursuant to Sections 13(a), 13(c), 14 and 15(d) of the
Securities Exchange Act of 1934, prior to the filing of a post-effective
amendment which indicates that all securities offered have been sold or which
deregisters all securities then remaining unsold, shall be deemed to be
incorporated by this reference in this registration statement and to be a part
hereof from the date of filing of such documents:

                (a)      The Registrant's Annual Report on Form 10-K, as
                         amended, for the fiscal year ended September 30,
                         1999.

                (b)      The Registrant's Quarterly Reports on Form 10-Q for
                         the quarters ended December 31, 1999, and March 31,
                         2000, as amended, and the Registrant's Current
                         Reports on Form 8-K, dated November 30, 1999, as
                         amended, February 25, 2000, and June 20, 2000.

                (c)      The description of the Registrant's common stock
                         contained in the registration statement filed by the
                         Registrant to register such securities under Section
                         12 of the Securities Exchange Act of 1934, including
                         any amendment or report filed for the purpose of
                         updating such description.

Item 4.         Description of Securities.

                Not applicable.

Item 5.         Interests of Named Experts and Counsel.

                Not applicable.

---------------------------------
(1) The information called for by Part I of this registration statement on Form
    S-8 is currently included in the Summary of the Registrant's Non-Qualified
    Stock Option Plan for Former Employees of Cadus Pharmaceutical Corp. and the
    Summary of the Registrant's 1999 Incentive and Non-Qualified Stock Option
    Plan (the "Plans") and will be delivered to eligible persons under the Plans
    as specified by Rule 428(b)(1) of the Securities Act of 1933, as amended.
    Pursuant to the Note to Part I of Form S-8, this information is not being
    filed with or included in this Form S-8.

<PAGE>   4

Item 6.           Indemnification of Directors and Officers.

                  Section 145 of the General Corporation Law of Delaware
empowers a corporation to indemnify any person who was or is a party or is
threatened to be made a party to any threatened, pending or completed action,
suit or proceeding, whether civil, criminal, administrative or investigative, by
reason of the fact that he or she is or was a director, officer, employee or
agent of the corporation or another enterprise if serving such enterprise at the
request of the corporation. Depending on the character of the proceeding, a
corporation may indemnify against expenses (including attorney's fees),
judgments, fines and amounts paid in settlement actually and reasonably incurred
in connection with such action, suit or proceeding if the person indemnified
acted in good faith and in a manner he or she reasonably believed to be in or
not opposed to the best interests of the corporation, and, with respect to any
criminal action or proceeding, had no reasonable cause to believe his or her
conduct was unlawful. In the case of an action by or in the right of the
corporation, no indemnification may be made in respect to any claim, issue or
matter as to which such person shall have been adjudged to be liable to the
corporation unless and only to the extent that the Court of Chancery or the
court in which such action or suit was brought shall determine that despite the
adjudication of liability, but in view of all the circumstances of the case,
such person is fairly and reasonably entitled to indemnity for such expenses
that the court shall deem proper. Section 145 further provides that to the
extent a director or officer of a corporation has been successful in the defense
of any action, suit or proceeding referred to above, or in defense of any claim,
issue or matter therein, he or she shall be indemnified against expenses
(including attorney's fees) actually and reasonably incurred by him or her in
connection therewith.

                  The Registrant's Certificate of Incorporation provides that
the Registrant shall, to the fullest extent authorized by the General
Corporation Law of Delaware, indemnify any person, or the legal representative
of any person, who is or was a director, officer, employee or agent of the
Registrant or another enterprise if said person served such enterprise at the
request of the Registrant. The Certificate of Incorporation also provides that
any amendment to the General Corporation Law of Delaware shall only be
applicable to the extent any such amendment permits the Registrant to provide
broader indemnification rights than said law permitted the Registrant to provide
prior to such amendment. The Certificate of Incorporation further provides that
in the case of an action, suit or proceeding initiated by the indemnified
person, the Registrant shall indemnify the person only if such action, suit or
proceeding was authorized by the Registrant's Board of Directors. The
Certificate of Incorporation also contains a provision eliminating the liability
of directors of the Registrant to itself or its stockholders for monetary
damages for breach of fiduciary duty except under certain specified
circumstances. The Certificate of Incorporation also permits the Registrant to
maintain insurance to protect itself and any director, officer, employee or
agent against any liability with respect to which the Registrant would have the
power to indemnify such persons under the General Corporation Law of Delaware.
The Registrant maintains an insurance policy insuring its directors and officers
against certain liabilities.

Item 7.           Exemption from Registration Claimed.

                  Not applicable.

<PAGE>   5

Item 8.           Exhibits.

                  The following is a list of exhibits filed as part of the
                  registration statement:

                  4.1      Non-Qualified Stock Option Plan for Former Employees
                           of Cadus Pharmaceutical Corp.

                  4.2      1999 Incentive and Non-Qualified Stock Option Plan.

                  5        Opinion of Saul, Ewing, Remick & Saul LLP.

                  23.1     Consent of KPMG LLP, independent public accountants.

                  23.2     Consent of Saul, Ewing, Remick & Saul LLP (contained
                           in Exhibit No. 5).

                  24       Power of Attorney (included on signature page of the
                           registration statement).

Item 9.           Undertakings.

                  (a)      The undersigned Registrant hereby undertakes:

                           (1)      to file, during any period in which offers
                  or sales are being made, a post-effective amendment to this
                  registration statement;

                                    (i)     to include any prospectus required
                           by section 10(a)(3) of the Securities Act of 1933;

                                    (ii)    to reflect in the prospectus any
                           facts or events arising after the effective date of
                           the registration statement (or the most recent
                           post-effective amendment thereof) which, individually
                           or in the aggregate, represent a fundamental change
                           in the information set forth in the registration
                           statement. Notwithstanding the foregoing, any
                           increase or decrease in volume of securities offered
                           (if the total dollar value of securities offered
                           would not exceed that which was registered) and any
                           deviation from the low or high end of the estimated
                           maximum offering range may be reflected in the form
                           of prospectus filed with the Commission pursuant to
                           Rule 424(b) if, in the aggregate, the changes in
                           volume and price represent no more than a 20% change
                           in the maximum aggregate offering price set forth in
                           the "Calculation of Registration Fee" table in the
                           effective registration statement.

                                    (iii)   To include any material information
                           with respect to the plan of distribution not
                           previously disclosed in the registration statement or
                           any material change to such information in the
                           registration statement;

                           Provided, however, that paragraphs (1)(i) and (1)(ii)
                           above do not apply if the registration statement is
                           on Form S-3 or Form S-8, and the information required
                           to be included in a post-effective amendment by those
                           paragraphs is contained in periodic reports filed by
                           the registrant pursuant to section 13 or

<PAGE>   6

                           section 15(d) of the Securities Exchange Act of 1934
                           that are incorporated by reference in the
                           registration statement.

                           (2)      That, for the purpose of determining any
                  liability under the Securities Act of 1933, each such
                  post-effective amendment shall be deemed to be a new
                  registration statement relating to the securities offered
                  therein, and the offering of such securities at that time
                  shall be deemed to be the initial bona fide offering thereof.

                           (3)      To remove from registration by means of a
                  post-effective amendment any of the securities being
                  registered which remain unsold at the termination of the
                  offering.

                  (b)      The undersigned Registrant hereby undertakes that,
         for purposes of determining any liability under the Securities Act of
         1933, each filing of the Registrant's annual report pursuant to Section
         13(a) or Section 15(d) of the Securities Exchange Act of 1934 that is
         incorporated by reference in this registration statement shall be
         deemed to be a new registration statement relating to the securities
         offered therein, and the offering of such securities at that time shall
         be deemed to be the initial bona fide offering thereof.

                  (c)      Insofar as indemnification for liabilities arising
         under the Securities Act of 1933 may be permitted to directors,
         officers and controlling persons of the Registrant pursuant to the
         foregoing provisions, or otherwise, the Registrant has been advised
         that in the opinion of the Securities and Exchange Commission such
         indemnification is against public policy as expressed in the Act and
         is, therefore, unenforceable. In the event that a claim for
         indemnification against such liability (other than payment by the
         Registrant of expenses incurred or paid by a director, officer or
         controlling person of the Registrant in the successful defense of any
         action, suit or proceeding) is asserted by such director, officer or
         controlling person in connection with the securities being registered,
         the Registrant will, unless in the opinion of its counsel the matter
         has been settled by controlling precedent, submit to a court of
         appropriate jurisdiction the question whether such indemnification by
         it is against public policy as expressed in the Act and will be
         governed by the final adjudication of such issue.

<PAGE>   7

                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this registration
statement to be signed on its behalf by the undersigned, thereunder duly
authorized, in the City of Uniondale, State of New York, on July 21, 2000.

                                       OSI PHARMACEUTICALS, INC.

                                       By: /s/ Colin Goddard, Ph.D.
                                           -------------------------------------
                                           Colin Goddard, Ph.D.
                                           President and Chief Executive Officer

                                POWER OF ATTORNEY

                  KNOW ALL MEN BY THESE PRESENTS, that each person whose
signature appears below hereby makes, constitutes and appoints Colin Goddard,
Ph.D. and Robert L. Van Nostrand and each of them, with full power to act
without the other, his true and lawful attorneys-in-fact and agents with full
power of substitution and resubstitution, for him and in his name, place and
stead, in any and all capacities to sign any and all amendments to this
registration statement on Form S-8, including post-effective amendments, and to
file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, granting unto said
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
connection therewith, as fully to all intents and purposes as he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or any substitute or substitutes, may lawfully do or
cause to be done by virtue hereof.

                  Pursuant to the requirements of the Securities Act of 1933,
this registration statement has been signed by the following persons in the
capacities and on the dates indicated.

<TABLE>
<CAPTION>
              Signature                                                  Title                      Date
              ---------                                                  -----                      ----

<S>                                                            <C>                             <C>
/s/ COLIN GODDARD, Ph.D.                                             President and             July 21, 2000
-------------------------------------------------               Chief Executive Officer
Colin Goddard, Ph.D.                                                 and Director

/s/ ROBERT L. VAN NOSTRAND                                       Vice President, Chief         July 26, 2000
-------------------------------------------------                  Financial Officer
Robert L. Van Nostrand                                         (principal financial and
                                                                  accounting officer)

/s/ GARY E. FRASHIER                                                  Chairman of              July 26, 2000
-------------------------------------------------               the Board of Directors
Gary E. Frashier
</TABLE>

<PAGE>   8
<TABLE>
<S>                                                            <C>                             <C>
                                                                       Director                ___________
-------------------------------------------------
G. Morgan Browne


JOHN H. FRENCH, II                                                     Director                July 24, 2000
-------------------------------------------------
John H. French, II

/s/ EDWIN A. GEE, PH.D                                                 Director                July 22, 2000
-------------------------------------------------
Edwin A. Gee, Ph.D.

/s/ DARYL K. GRANNER, M.D.                                             Director                July 21, 2000
-------------------------------------------------
Daryl K. Granner, M.D.

/s/ WALTER M. LOVENBERG, PH.D.                                         Director                July 26, 2000
-------------------------------------------------
Walter M. Lovenberg, Ph.D.

/s/ VIREN MEHTA                                                        Director                July 25, 2000
-------------------------------------------------
Viren Mehta

/s/ STEVEN M. PELTZMAN                                                 Director                July 24, 2000
-------------------------------------------------
Steven M. Peltzman

/s/ SIR MARK RICHMOND, PH.D                                            Director                July 24, 2000
-------------------------------------------------
Sir Mark Richmond, Ph.D.

/s/ JOHN P. WHITE, ESQUIRE                                             Director                July 24, 2000
-------------------------------------------------
John P. White, Esquire
</TABLE>

<PAGE>   9

                                  EXHIBIT INDEX
                                  -------------

<TABLE>
<CAPTION>

EXHIBIT NO.                                                    EXHIBIT
-----------                                                    -------

<S>                                   <C>
4.1                                   Non-Qualified Stock Option Plan for Former Employees of Cadus
                                      Pharmaceutical Corp.

4.2                                   1999 Incentive and Non-Qualified Stock Option Plan.

5                                     Opinion of Saul, Ewing, Remick & Saul LLP.

23.1                                  Consent of KPMG LLP, independent public accountants.

23.2                                  Consent of Saul, Ewing, Remick & Saul LLP (contained in Exhibit No. 5).

                                      Power of Attorney (included on signature page of the registration
24                                    statement).
</TABLE>
[{"type": "S-8", "sequence": "1", "filename": "s-8.txt", "description": "OSI PHARMACEUTICALS, INC.", "secsgml_size_bytes": 24617}]
{"company-data": {"conformed-name": "OSI PHARMACEUTICALS INC", "cik": "0000729922", "assigned-sic": "2835", "irs-number": "133159796", "state-of-incorporation": "DE", "fiscal-year-end": "0930"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-42274", "film-number": "679373"}, "business-address": {"street1": "106 CHARLES LINDBERGH BLVD", "city": "UNIONDALE", "state": "NY", "zip": "11553", "phone": "5162220023"}, "mail-address": {"street1": "106 CHARLES LINDBERGH BLVD", "city": "UNIONDALE", "state": "NY", "zip": "11553-3649"}, "former-company": {"former-conformed-name": "ONCOGENE SCIENCE INC", "date-changed": "19920703"}}
1

      As filed with the Securities and Exchange Commission on July 26, 2000

                                                 Registration No. ______________

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      under
                           THE SECURITIES ACT OF 1933
                             -----------------------

                            OSI PHARMACEUTICALS, INC.
             (Exact name of registrant as specified in its charter)
                             -----------------------
Delaware                               13-3159796
                        ------------------------------              --------------------------
                       (State or other jurisdiction of                 (I.R.S. Employer
                        incorporation or organization)                Identification No.)

                          106 Charles Lindbergh Blvd.
                                 Uniondale, NY                                11553
                        ------------------------------              --------------------------
                    (Address of principal executive offices)               (Zip Code)
-----------------------
                            OSI PHARMACEUTICALS, INC.
                         NON-QUALIFIED STOCK OPTION PLAN
                             FOR FORMER EMPLOYEES OF
                           CADUS PHARMACEUTICAL CORP.
                                       AND
                            OSI PHARMACEUTICALS, INC.
                               1999 INCENTIVE AND
                                  NON-QUALIFIED
                                STOCK OPTION PLAN
                            (Full title of the plan)
                             -----------------------
                             ROBERT L. VAN NOSTRAND
                   VICE PRESIDENT AND CHIEF FINANCIAL OFFICER
                            OSI PHARMACEUTICALS, INC.
                           106 CHARLES LINDBERGH BLVD.
                            UNIONDALE, NEW YORK 11553
                                 (516) 222-0023
            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)
                             -----------------------

                                    Copy to:

                         SPENCER W. FRANCK, JR., ESQUIRE
                         SAUL, EWING, REMICK & SAUL LLP
                               CENTRE SQUARE WEST
                         1500 MARKET STREET, 38TH FLOOR
                        PHILADELPHIA, PENNSYLVANIA 19102
                                 (215) 972-1955
                             -----------------------
               See next page for calculation of registration fee.
                             -----------------------
2

                         CALCULATION OF REGISTRATION FEE
=====================================================================================================================
                                         Proposed Maximum   Proposed Maximum
 Title of Securities     Amount to be    Offering Price        Aggregate
   to be Registered       Registered        Per Share       Offering Price        Amount of Registration Fee (5)
---------------------------------------------------------------------------------------------------------------------
Common Stock, Par         334,632(1)         $ 5.0000      $   1,673,160.00
Value $.01 Per Share       25,000(2)         $14.0000      $     350,000.00
                          742,125(3)         $23.2500      $  17,254,406.25
                        1,257,875(4)         $31.78125     $  39,976,839.84                  $15,643.16
                        ---------                             -------------                   =========
                        2,359,632                                  X.000264
                        =========                           ===============
=====================================================================================================================
(1)      Represents shares issuable upon exercise of options previously granted
         under the Non-Qualified Stock Option Plan for Former Employees of Cadus
         Pharmaceutical Corp. (the "Cadus Plan").
(2)      Represents shares issuable upon exercise of options previously granted
         under the Cadus Plan.
(3)      Represents shares issuable upon exercise of options previously granted
         under the 1999 Incentive and Non-Qualified Stock Option Plan (the "1999
         Plan").
(4)      Represents shares issuable in connection with options available for
         grant under the 1999 Plan.
(5)      The registration fee has been computed in accordance with paragraphs
         (c) and (h) of Rule 457, based upon, in the case of options previously
         granted, the stated exercise price of such options, and, in the case of
         options still available for grant, the average of the reported high and
         low sale prices of shares of the Registrant's common stock on July 20,
         2000.
3

                                  PART I

             INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

Item 1.        Plan Information.(1)

Item 2.        Registrant Information and Employee Plan Annual Information.(1)

                                  PART II

             INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.        Incorporation of Documents by Reference.

               The documents listed in clauses (a), (b) and (c) below are
incorporated herein by this reference thereto, and all documents subsequently
filed by the Registrant pursuant to Sections 13(a), 13(c), 14 and 15(d) of the
Securities Exchange Act of 1934, prior to the filing of a post-effective
amendment which indicates that all securities offered have been sold or which
deregisters all securities then remaining unsold, shall be deemed to be
incorporated by this reference in this registration statement and to be a part
hereof from the date of filing of such documents:

                (a)      The Registrant's Annual Report on Form 10-K, as
                         amended, for the fiscal year ended September 30,
                         1999.

                (b)      The Registrant's Quarterly Reports on Form 10-Q for
                         the quarters ended December 31, 1999, and March 31,
                         2000, as amended, and the Registrant's Current
                         Reports on Form 8-K, dated November 30, 1999, as
                         amended, February 25, 2000, and June 20, 2000.

                (c)      The description of the Registrant's common stock
                         contained in the registration statement filed by the
                         Registrant to register such securities under Section
                         12 of the Securities Exchange Act of 1934, including
                         any amendment or report filed for the purpose of
                         updating such description.

Item 4.         Description of Securities.

                Not applicable.

Item 5.         Interests of Named Experts and Counsel.

                Not applicable.

---------------------------------
(1) The information called for by Part I of this registration statement on Form
    S-8 is currently included in the Summary of the Registrant's Non-Qualified
    Stock Option Plan for Former Employees of Cadus Pharmaceutical Corp. and the
    Summary of the Registrant's 1999 Incentive and Non-Qualified Stock Option
    Plan (the "Plans") and will be delivered to eligible persons under the Plans
    as specified by Rule 428(b)(1) of the Securities Act of 1933, as amended.
    Pursuant to the Note to Part I of Form S-8, this information is not being
    filed with or included in this Form S-8.
4

Item 6.           Indemnification of Directors and Officers.

                  Section 145 of the General Corporation Law of Delaware
empowers a corporation to indemnify any person who was or is a party or is
threatened to be made a party to any threatened, pending or completed action,
suit or proceeding, whether civil, criminal, administrative or investigative, by
reason of the fact that he or she is or was a director, officer, employee or
agent of the corporation or another enterprise if serving such enterprise at the
request of the corporation. Depending on the character of the proceeding, a
corporation may indemnify against expenses (including attorney's fees),
judgments, fines and amounts paid in settlement actually and reasonably incurred
in connection with such action, suit or proceeding if the person indemnified
acted in good faith and in a manner he or she reasonably believed to be in or
not opposed to the best interests of the corporation, and, with respect to any
criminal action or proceeding, had no reasonable cause to believe his or her
conduct was unlawful. In the case of an action by or in the right of the
corporation, no indemnification may be made in respect to any claim, issue or
matter as to which such person shall have been adjudged to be liable to the
corporation unless and only to the extent that the Court of Chancery or the
court in which such action or suit was brought shall determine that despite the
adjudication of liability, but in view of all the circumstances of the case,
such person is fairly and reasonably entitled to indemnity for such expenses
that the court shall deem proper. Section 145 further provides that to the
extent a director or officer of a corporation has been successful in the defense
of any action, suit or proceeding referred to above, or in defense of any claim,
issue or matter therein, he or she shall be indemnified against expenses
(including attorney's fees) actually and reasonably incurred by him or her in
connection therewith.

                  The Registrant's Certificate of Incorporation provides that
the Registrant shall, to the fullest extent authorized by the General
Corporation Law of Delaware, indemnify any person, or the legal representative
of any person, who is or was a director, officer, employee or agent of the
Registrant or another enterprise if said person served such enterprise at the
request of the Registrant. The Certificate of Incorporation also provides that
any amendment to the General Corporation Law of Delaware shall only be
applicable to the extent any such amendment permits the Registrant to provide
broader indemnification rights than said law permitted the Registrant to provide
prior to such amendment. The Certificate of Incorporation further provides that
in the case of an action, suit or proceeding initiated by the indemnified
person, the Registrant shall indemnify the person only if such action, suit or
proceeding was authorized by the Registrant's Board of Directors. The
Certificate of Incorporation also contains a provision eliminating the liability
of directors of the Registrant to itself or its stockholders for monetary
damages for breach of fiduciary duty except under certain specified
circumstances. The Certificate of Incorporation also permits the Registrant to
maintain insurance to protect itself and any director, officer, employee or
agent against any liability with respect to which the Registrant would have the
power to indemnify such persons under the General Corporation Law of Delaware.
The Registrant maintains an insurance policy insuring its directors and officers
against certain liabilities.

Item 7.           Exemption from Registration Claimed.

                  Not applicable.
5

Item 8.           Exhibits.

                  The following is a list of exhibits filed as part of the
                  registration statement:

                  4.1      Non-Qualified Stock Option Plan for Former Employees
                           of Cadus Pharmaceutical Corp.

                  4.2      1999 Incentive and Non-Qualified Stock Option Plan.

                  5        Opinion of Saul, Ewing, Remick & Saul LLP.

                  23.1     Consent of KPMG LLP, independent public accountants.

                  23.2     Consent of Saul, Ewing, Remick & Saul LLP (contained
                           in Exhibit No. 5).

                  24       Power of Attorney (included on signature page of the
                           registration statement).

Item 9.           Undertakings.

                  (a)      The undersigned Registrant hereby undertakes:

                           (1)      to file, during any period in which offers
                  or sales are being made, a post-effective amendment to this
                  registration statement;

                                    (i)     to include any prospectus required
                           by section 10(a)(3) of the Securities Act of 1933;

                                    (ii)    to reflect in the prospectus any
                           facts or events arising after the effective date of
                           the registration statement (or the most recent
                           post-effective amendment thereof) which, individually
                           or in the aggregate, represent a fundamental change
                           in the information set forth in the registration
                           statement. Notwithstanding the foregoing, any
                           increase or decrease in volume of securities offered
                           (if the total dollar value of securities offered
                           would not exceed that which was registered) and any
                           deviation from the low or high end of the estimated
                           maximum offering range may be reflected in the form
                           of prospectus filed with the Commission pursuant to
                           Rule 424(b) if, in the aggregate, the changes in
                           volume and price represent no more than a 20% change
                           in the maximum aggregate offering price set forth in
                           the "Calculation of Registration Fee" table in the
                           effective registration statement.

                                    (iii)   To include any material information
                           with respect to the plan of distribution not
                           previously disclosed in the registration statement or
                           any material change to such information in the
                           registration statement;

                           Provided, however, that paragraphs (1)(i) and (1)(ii)
                           above do not apply if the registration statement is
                           on Form S-3 or Form S-8, and the information required
                           to be included in a post-effective amendment by those
                           paragraphs is contained in periodic reports filed by
                           the registrant pursuant to section 13 or
6

                           section 15(d) of the Securities Exchange Act of 1934
                           that are incorporated by reference in the
                           registration statement.

                           (2)      That, for the purpose of determining any
                  liability under the Securities Act of 1933, each such
                  post-effective amendment shall be deemed to be a new
                  registration statement relating to the securities offered
                  therein, and the offering of such securities at that time
                  shall be deemed to be the initial bona fide offering thereof.

                           (3)      To remove from registration by means of a
                  post-effective amendment any of the securities being
                  registered which remain unsold at the termination of the
                  offering.

                  (b)      The undersigned Registrant hereby undertakes that,
         for purposes of determining any liability under the Securities Act of
         1933, each filing of the Registrant's annual report pursuant to Section
         13(a) or Section 15(d) of the Securities Exchange Act of 1934 that is
         incorporated by reference in this registration statement shall be
         deemed to be a new registration statement relating to the securities
         offered therein, and the offering of such securities at that time shall
         be deemed to be the initial bona fide offering thereof.

                  (c)      Insofar as indemnification for liabilities arising
         under the Securities Act of 1933 may be permitted to directors,
         officers and controlling persons of the Registrant pursuant to the
         foregoing provisions, or otherwise, the Registrant has been advised
         that in the opinion of the Securities and Exchange Commission such
         indemnification is against public policy as expressed in the Act and
         is, therefore, unenforceable. In the event that a claim for
         indemnification against such liability (other than payment by the
         Registrant of expenses incurred or paid by a director, officer or
         controlling person of the Registrant in the successful defense of any
         action, suit or proceeding) is asserted by such director, officer or
         controlling person in connection with the securities being registered,
         the Registrant will, unless in the opinion of its counsel the matter
         has been settled by controlling precedent, submit to a court of
         appropriate jurisdiction the question whether such indemnification by
         it is against public policy as expressed in the Act and will be
         governed by the final adjudication of such issue.
7

                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this registration
statement to be signed on its behalf by the undersigned, thereunder duly
authorized, in the City of Uniondale, State of New York, on July 21, 2000.

                                       OSI PHARMACEUTICALS, INC.

                                       By: /s/ Colin Goddard, Ph.D.
                                           -------------------------------------
                                           Colin Goddard, Ph.D.
                                           President and Chief Executive Officer

                                POWER OF ATTORNEY

                  KNOW ALL MEN BY THESE PRESENTS, that each person whose
signature appears below hereby makes, constitutes and appoints Colin Goddard,
Ph.D. and Robert L. Van Nostrand and each of them, with full power to act
without the other, his true and lawful attorneys-in-fact and agents with full
power of substitution and resubstitution, for him and in his name, place and
stead, in any and all capacities to sign any and all amendments to this
registration statement on Form S-8, including post-effective amendments, and to
file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, granting unto said
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
connection therewith, as fully to all intents and purposes as he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents or any of them, or any substitute or substitutes, may lawfully do or
cause to be done by virtue hereof.

                  Pursuant to the requirements of the Securities Act of 1933,
this registration statement has been signed by the following persons in the
capacities and on the dates indicated.
Signature                                                  Title                      Date
              ---------                                                  -----                      ----
/s/ COLIN GODDARD, Ph.D.                                             President and             July 21, 2000
-------------------------------------------------               Chief Executive Officer
Colin Goddard, Ph.D.                                                 and Director

/s/ ROBERT L. VAN NOSTRAND                                       Vice President, Chief         July 26, 2000
-------------------------------------------------                  Financial Officer
Robert L. Van Nostrand                                         (principal financial and
                                                                  accounting officer)

/s/ GARY E. FRASHIER                                                  Chairman of              July 26, 2000
-------------------------------------------------               the Board of Directors
Gary E. Frashier
8
Director                ___________
-------------------------------------------------
G. Morgan Browne

JOHN H. FRENCH, II                                                     Director                July 24, 2000
-------------------------------------------------
John H. French, II

/s/ EDWIN A. GEE, PH.D                                                 Director                July 22, 2000
-------------------------------------------------
Edwin A. Gee, Ph.D.

/s/ DARYL K. GRANNER, M.D.                                             Director                July 21, 2000
-------------------------------------------------
Daryl K. Granner, M.D.

/s/ WALTER M. LOVENBERG, PH.D.                                         Director                July 26, 2000
-------------------------------------------------
Walter M. Lovenberg, Ph.D.

/s/ VIREN MEHTA                                                        Director                July 25, 2000
-------------------------------------------------
Viren Mehta

/s/ STEVEN M. PELTZMAN                                                 Director                July 24, 2000
-------------------------------------------------
Steven M. Peltzman

/s/ SIR MARK RICHMOND, PH.D                                            Director                July 24, 2000
-------------------------------------------------
Sir Mark Richmond, Ph.D.

/s/ JOHN P. WHITE, ESQUIRE                                             Director                July 24, 2000
-------------------------------------------------
John P. White, Esquire
9

                                  EXHIBIT INDEX
                                  -------------
EXHIBIT NO.                                                    EXHIBIT
-----------                                                    -------
4.1                                   Non-Qualified Stock Option Plan for Former Employees of Cadus
                                      Pharmaceutical Corp.

4.2                                   1999 Incentive and Non-Qualified Stock Option Plan.

5                                     Opinion of Saul, Ewing, Remick & Saul LLP.

23.1                                  Consent of KPMG LLP, independent public accountants.

23.2                                  Consent of Saul, Ewing, Remick & Saul LLP (contained in Exhibit No. 5).

                                      Power of Attorney (included on signature page of the registration
24                                    statement).