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                    [WILMER, CUTLER & PICKERING LETTERHEAD]

                                                                     EXHIBIT 5.3

                               September 14, 2000

Tyco International Ltd.
The Zurich Centre, Second Floor
90 Pitts Bay Road
Pembroke HM08
Bermuda

Tyco International Group S.A.
6, avenue Emile Reuter
Second Floor
L- 2420 Luxembourg

Ladies and Gentlemen:

    We have acted as United States securities counsel for Tyco
International Ltd., a Bermuda company ("Tyco"), and Tyco International Group
S.A., a Luxembourg company (the "Issuer"), in connection with the filing by Tyco
and the Issuer with the United States Securities and Exchange Commission (the
"Commission") of a Registration Statement on Form S-3, File Nos. 333-44100 and
333-44100-01 (as amended, the "Registration Statement"), with respect to the
Issuer's (i) unsecured debt securities (the "Debt Securities"), (ii) guarantees
(the "Guarantees") and (iii) common shares to be issued upon conversion or
exchange of the Debt Securities by Tyco (the "Common Shares"), to be issued from
time to time pursuant to Rule 415 under the United States Securities Act of
1933, as amended (the "Securities Act"), for an aggregate initial offering price
not to exceed US$3,500,000,000. The Debt Securities are to be issued in one or
more series pursuant to Indentures among the Issuer, Tyco (as Guarantor) and the
trustees thereunder (the "Trustees").

    We have examined (i) the form of Senior Indenture filed as Exhibit 4.1 to
Post-Effective Amendment No. 1 to the registration statement dated June 9, 1998,
pursuant to which Debt Securities may be issued; (ii) the form of Subordinated
Indenture filed as Exhibit 4.2 to the Registration Statement, pursuant to which
Debt Securities may be issued (together with the Senior Indenture, the
"Indentures"); (iii) the Registration Statement; and (iv) originals, photocopies
or conformed copies of all such records of Tyco, the Issuer and their
subsidiaries, all such agreements and certificates of public officials, and such
other documents as we have deemed relevant and necessary as a basis for the
opinion hereinafter expressed. In addition, we have examined and relied upon the
opinions of Appleby Spurling & Kempe, Bermuda counsel to Tyco, with respect to
the authorization of Tyco to issue the Guarantees and the authorization and
validity upon issuance of Tyco's Common Shares, and Beghin & Feider, Luxembourg
counsel to the Issuer, with respect to the Issuer's authorization to issue the
Debt Securities.

    In connection with this opinion, we have assumed that (i) the Registration
Statement, and any amendments thereto (including post-effective amendments),
will have become effective; (ii) a prospectus supplement will have been prepared
and filed with the Commission describing the Debt Securities offered thereby and
the Guarantees; (iii) all Debt Securities will be issued and sold in the manner
stated in the Registration Statement and the appropriate prospectus supplement;
(iv) the Indentures and any applicable supplemental indentures will have been
duly authorized, executed and delivered by the Issuer, Tyco and the Trustees,
and any such supplemental indentures will conform to the Indentures and to
applicable law; (v) a definitive purchase, underwriting or similar agreement
with respect to any Debt Securities offered will have been duly authorized,
validly executed and delivered by the Issuer, Tyco and the other parties
thereto; and (vi) any Common Shares issuable upon conversion or exchange of the
Debt Securities being offered will be duly authorized, created and, if
applicable, reserved for issuance upon such conversion or exchange.
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Tyco International Ltd.
Tyco International Group S.A.
September 14, 2000
Page 2

    Based upon and subject to the foregoing, we are of the opinion that:

    With respect to Debt Securities to be issued under the Indenture, when
(i) the applicable Indenture has been duly qualified under the Trust Indenture
Act of 1939, as amended; (ii) the Board of the Issuer has taken all necessary
corporate action to approve the issuance and terms of such Debt Securities, the
terms of the offering thereof and related matters; and (iii) such Debt
Securities have been duly executed, authenticated, issued and delivered in
accordance with the provisions of the applicable Indenture, the applicable
supplemental indenture and the provisions of the applicable definitive purchase,
underwriting or similar agreement approved by authorization of the Board of the
Issuer upon payment of the consideration therefor provided for therein such Debt
Securities will be legally issued and will constitute valid and binding
obligations of the Issuer, enforceable against the Issuer in accordance with
their terms, except as such enforcement is subject to any applicable bankruptcy,
insolvency, reorganization or other laws relating to or affecting creditors'
rights generally and general principles of equity.

    With respect to the Guarantees, when (i) the Board of Tyco has taken all
necessary corporate action to approve the creation of and the issuance and terms
of the Guarantees and related matters; and (ii) the Guarantees have been duly
executed, authenticated, issued and delivered by Tyco in accordance with the
Indentures, such Guarantees will be legally issued and will constitute valid and
binding obligations of Tyco, enforceable against Tyco in accordance with their
terms, except as such enforcement is subject to any applicable bankruptcy,
insolvency, reorganization or other laws relating to or affecting creditors'
rights generally and general principles of equity.

    We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the statements made with respect to us under the
caption "Legal Matters" in the Prospectus included as part of the Registration
Statement.

    In rendering the foregoing opinion, we do not express an opinion concerning
any laws other than the laws of the State of New York and the federal laws of
the United States of America.

                                          Sincerely,

                                          WILMER, CUTLER & PICKERING

                                          By: /s/ MEREDITH B. CROSS
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                                             Meredith B. Cross, a Partner