EXHIBIT 5.1


                                  July 31, 2001




Fair, Isaac and Company, Incorporated
200 Smith Ranch Road
San Rafael, CA  94903




         Re:  Registration  Statement on Form S-8 for Certain  Option  Grants by
              Fair, Isaac and Company,  Incorporated to Thomas G. Grudnowski and
              Mark Pautsch



Ladies and Gentlemen:


         With reference to the Registration Statement on Form S-8 to be filed by
Fair, Isaac and Company,  Incorporated,  a Delaware corporation (the "Company"),
with the  Securities  and Exchange  Commission  under the Securities Act of 1933
relating to 247,500 shares of the Company's Common Stock issuable  pursuant to a
Nonstatutory Stock Option Agreement between the Company and Thomas G. Grudnowski
and a Nonstatutory  Stock Option Agreement  between the Company and Mark Pautsch
(the  "Agreements"),  it is our opinion  that such shares of the Common Stock of
the Company,  when issued and sold in accordance  with the  Agreements,  will be
legally issued, fully paid and nonassessable.

         We hereby consent to the filing of this opinion with the Securities and
Exchange  Commission  as  Exhibit  5.1  and  Exhibit  23.1  to the  Registration
Statement.

                                                   Very truly yours,

                                                   /s/ PILLSBURY WINTHROP LLP