<PAGE>

               UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549

                                  FORM 10-K/A

[X]  ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
     ACT OF 1934

For the fiscal year ended: December 31, 1999

                                       OR

[_]  TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES ACT
     OF 1934

For the transition period from __________ to _________.

Commission File Number: 333-46019-3

  GreenPoint Mortgage Securities Inc. (formerly Headlands Mortgage Securities
 Inc.) (as Sponsor under a Pooling and Servicing Agreement dated as of December
 1, 1998, among the Sponsor, GreenPoint Mortgage Funding, Inc. (formerly
 Headlands Mortgage Company, Inc.), as Seller and Master Servicer, and the Bank
 of New York, as Trustee, providing for the issuance of Mortgage Pass-Through
 Certificates Series 1998-3)

                      GREENPOINT MORTGAGE SECURITIES INC.
            (Exact Name of registrant as specified in its charter)

<TABLE>
<S>                                                                                   <C>
                                 Delaware                                                           68-0397342
          (State or other jurisdiction of incorporation or organization)              (I.R.S. employer identification no.)


                   700 Larkspur Landing Circle, Suite 240,                                              94939
                             Larkspur, California                                                    (Zip code)
                   (Address of principal executive offices)
</TABLE>
                                (415) 461-6790
             (Registrant's telephone number, including area code)
<TABLE>
<S>                                                                    <C>
Securities registered pursuant to Section 12(b) of the Act:            Securities registered pursuant to Section 12(g) of the Act:

                                None                                                              None
                          (Title of class)                                                  (Title of class)
</TABLE>

Indicate by check mark whether the Registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that the Registrant was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days. Yes [X]  No [_]

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of Registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [X]

State the aggregate market value of the voting stock held by non-affiliates of
Registrant. The aggregate market value shall be computed by reference to the
price at which the stock was sold, or the average bid and asked prices of such
stock, as of specified date within 60 days prior to the date of filing:

                                Not Applicable

                     Documents incorporated by reference:

                                Not Applicable
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                                    PART IV


ITEM 14 - EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K

          (a)  The following documents are filed as part of this report:

               3.   Exhibits:

                    Exhibit No.         Description
                    -----------         -----------

                    99.1*               Statement of Compliance of the Master
                                        Servicer pursuant to Section 3.13 of the
                                        Pooling and Servicing Agreement.

                    99.2                Annual Independent Public Accountant's
                                        Servicing Report with respect to the
                                        Master Servicer's and overall servicing
                                        operations pursuant to Section 3.14 of
                                        the Pooling Servicing Agreement.
___________________
*  Previously filed.
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                                   SIGNATURES


     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the Sponsor has duly caused this Report to be signed on
its behalf by the undersigned, thereunto duly authorized.


                                    By:  GREENPOINT MORTGAGE SECURITIES INC.,
                                         As Sponsor


                                         By:  /s/ Gilbert J. MacQuarrie
                                            ------------------------------------
                                         Name:  Gilbert J. MacQuarrie
                                         Title: Vice President, Chief Financial
                                                Officer and Secretary
Date: May 31, 2000.

     Pursuant to the requirements of the Securities Exchange Act of 1934, this
Report has been signed below by the following persons on behalf of the Sponsor
and in the capacities and on the dates indicated:

<TABLE>
<CAPTION>
          Signature                                           Position                                             Date
          ---------                                           --------                                             ----
<S>                                                    <C>                                                       <C>
/s/ S.A. Ibrahim                                       President and Director                                    May 31, 2000
-----------------------------------
S.A. Ibrahim                                           (Principal Executive Officer)


/s/ Becky S. Poisson                                   Vice President and Director                               May 31, 2000
-----------------------------------
Becky S. Poisson


/s/ Gilbert J. MacQuarrie                              Vice President, Chief Financial Officer, Secretary        May 31, 2000
-----------------------------------
Gilbert J. MacQuarrie                                  and Director


/s/ Steven M. Abreu                                    Vice President and Director                               May 31, 2000
-----------------------------------
Steven M. Abreu

                                                       Director                                                  May ___, 2000
-----------------------------------
Kenneth Siprelle

                                                       Director                                                  May ___, 2000
-----------------------------------
John Edmonds
</TABLE>
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                               INDEX TO EXHIBITS
                                  Item 14(C)

Exhibit No.    Description
-----------    -----------

99.1*          Statement of Compliance of the Master Servicer pursuant to
               Section 3.13 of the Pooling and Servicing Agreement.

99.2           Annual Independent Public Accountant's Servicing Report with
               respect to the Master Servicer's overall servicing operations
               pursuant to Section 3.14 of the Pooling and Servicing Agreement.

_____________________
*  Previously filed.