PROSPECTUS SUPPLEMENT
(TO PROSPECTUS DATED FEBRUARY 23, 2001)
--------------------------------------------------------------------------------
[UBS LOGO]
                                 $1,500,000,000
                          UBS PREFERRED FUNDING TRUST I
                 8.622% NONCUMULATIVE TRUST PREFERRED SECURITIES
                     REPRESENTING A CORRESPONDING AMOUNT OF
                8.622% NONCUMULATIVE COMPANY PREFERRED SECURITIES
                                       OF
                       UBS PREFERRED FUNDING COMPANY LLC I
                      GUARANTEED ON A SUBORDINATED BASIS BY
                                     UBS AG
--------------------------------------------------------------------------------

The following tax disclosure supplements, and to the extent inconsistent
therewith, replaces the disclosure set forth under the heading "Certain U.S. Tax
Considerations" in the attached prospectus:

         Under recently enacted legislation, dividends paid by a "qualified
         foreign corporation" to a non-corporate U.S. Holder prior to January 1,
         2009 are generally subject to a preferential rate of tax for U.S. tax
         purposes if the beneficial recipient of the dividend satisfies certain
         minimum holding period requirements and the dividend is paid out of the
         current or accumulated earnings and profits of the foreign corporation
         (as determined for U.S. federal income tax purposes). Although the
         matter is not free from doubt, the subordinated notes held by UBS
         Preferred Funding Company should be treated as stock of UBS AG.
         Furthermore, UBS AG should currently be treated as a "qualified foreign
         corporation" for U.S. federal income tax purposes. As discussed under
         "Certain U.S. Tax Considerations" in the attached prospectus, a U.S.
         Holder will generally include in income its allocable share of the
         income recognized by UBS Preferred Funding Company. Accordingly,
         amounts included in income by a non-corporate U.S. Holder with respect
         to its trust preferred securities prior to January 1, 2009 should
         generally be subject to a preferential rate of tax for U.S. tax
         purposes as long as (a) UBS Preferred Funding Company holds no assets
         other than the subordinated notes, (b) the U.S. Holder satisfies
         certain minimum holding period requirements and (c) the payments on the
         subordinated notes are paid out of the current or accumulated earnings
         and profits of UBS AG. Special rules will apply in determining the
         foreign tax credit limitation with respect to dividends that are
         subject to tax at a preferential rate.

         The discussion in the preceding paragraph is a summary of current law
         and it is possible that the law could be changed in a manner that would
         adversely affect a holder of trust preferred securities. In particular,
         although UBS AG should currently be treated as a "qualified foreign
         corporation", it is possible that regulations will be issued under
         which UBS AG would not be treated as a "qualified foreign corporation"
         for all periods after the issuance of such regulations. Holders of
         trust preferred securities are urged to consult their tax advisors as
         to the application of the recently enacted legislation with respect to
         their particular circumstances.

UBS Warburg LLC                         PaineWebber Incorporated

Credit Suisse First Boston

          Goldman, Sachs & Co.

                    Merrill Lynch & Co.

                              Morgan Stanley Dean Witter

                                        Salomon Smith Barney

Prospectus Supplement dated June 5, 2003