Exhibit 8.1


                                                               December 19, 2002



UBS AG,
         Bahnhofstrasse 45,
                  Zurich,
                           Switzerland.

UBS Preferred Funding Trust IV,
         c/o Wilmington Trust Company,
                  1100 North Market Street,
                           Wilmington, Delaware 19890.

UBS Preferred Funding Trust V,
         c/o Wilmington Trust Company,
                  1100 North Market Street,
                           Wilmington, Delaware 19890.


Ladies and Gentlemen:

                  As counsel to UBS AG (the "Company"), UBS Preferred Funding
Trust IV and UBS Preferred Funding Trust V (together with UBS Preferred Funding
Trust IV, the "UBS Preferred Funding Trusts") in connection with the
registration of up to $4,529,508,000 aggregate offering price of the debt
securities and warrants to be issued (on a delayed and continuous basis) by the
Company and of up to $4,529,508,000 aggregate offering price of the trust
preferred securities to be issued (on a delayed and continuous basis) by the UBS
Preferred Funding Trusts, in each case, pursuant to each base prospectus (each a
"Prospectus") which forms a part of the registration statement on Form F-3 of
the Company (such registration statement also constituting a pre-effective
amendment No. 2 to registration statement No. 333-64844 and post-effective
amendment No. 4 (as amended) to registration statement No. 333-46930)and the UBS
Preferred Funding Trusts filed with

the Securities and Exchange Commission on December 19, 2002 (the "Registration
Statement") to which this opinion is filed as an exhibit thereto, we hereby
confirm to you that the discussions set forth under the heading "U.S. Tax
Considerations" contained in each Prospectus in the Registration Statement is
our opinion, subject to the limitations set forth therein.

                  We hereby consent to the filing of this opinion as an exhibit
to the Registration Statement and to each reference to us under the heading
"U.S. Tax Considerations" in each Prospectus in the Registration Statement. In
giving such consent, we do not thereby admit that we are in the category of
persons whose consent is required under Section 7 of the Securities Act of 1933.

                                          Very truly yours,



                                          /s/ Sullivan & Cromwell