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                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

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                                    FORM 8-K

                                 CURRENT REPORT
                        PURSUANT TO SECTION 13 OR 15(D)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

                Date of Report (Date of earliest event reported)

                                February 4, 2002

                                   001-13836
                            (Commission File Number)

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                            TYCO INTERNATIONAL LTD.

             (Exact name of registrant as specified in its charter)

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                BERMUDA                                   NOT APPLICABLE
    (Jurisdiction of Incorporation)            (IRS Employer Identification Number)
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  THE ZURICH CENTRE, SECOND FLOOR, 90 PITTS BAY ROAD, PEMBROKE, HM 08, BERMUDA
              (Address of registrant's principal executive office)

                                  441-292-8674
                        (Registrant's telephone number)

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ITEM 5.  OTHER EVENTS

    On February 4, 2002, Tyco International Ltd., a Bermuda company, issued the
attached press release.

ITEM 7.  FINANCIAL STATEMENTS AND EXHIBITS

    (c) Exhibits

    99.1  Press Release of Tyco International Ltd., dated February 4, 2002.

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                                   SIGNATURES

    Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized.

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                                                       TYCO INTERNATIONAL LTD.

                                                       By:  /s/ MARK H. SWARTZ
                                                            -----------------------------------------
                                                            Mark H. Swartz
                                                            Executive Vice President and
                                                            Chief Financial Officer
                                                            (Principal Accounting and Financial
                                                            Officer)
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Dated: February 6, 2002

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                                 EXHIBIT INDEX

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       EXHIBIT
       NUMBER           DESCRIPTION
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        99.1            Press Release of Tyco International Ltd., dated February 4,
                          2002.
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