Filed Pursuant to Rule 424(b)(3) and (c)
File Number 333-108247

Prospectus Supplement No. 2
(To Prospectus Dated October 10, 2003)

ADC TELECOMMUNICATIONS, INC.

1.00% Convertible Subordinated Notes Due 2008
Floating Rate Convertible Subordinated Notes Due 2013
Common Stock Issuable Upon Conversion of the Notes

        This prospectus supplement relates to the resale by selling securityholders of their convertible notes and the shares of common stock issuable upon the conversion of the convertible notes.

        This prospectus supplement should be read in conjunction with, and may not be delivered or utilized without, the prospectus dated October 10, 2003 and any other amendments or supplements thereto. The terms of the convertible notes are set forth in the prospectus.

        The table below sets forth additional information concerning beneficial ownership of the convertible notes and supplements and amends the table appearing under the heading "Selling Securityholders" beginning on page 44 of the prospectus. To the extent that a selling security is listed both in the table below and in the table appearing in the prospectus, the information set forth below regarding the selling securityholder supersedes the information in the prospectus.

Name
   Principal Amount at Maturity of Notes Beneficially Owned Prior to this Offering (In Thousands)(1)
   Principal Amount at Maturity of Notes Beneficially Owned that May Be Sold (In Thousands)(1)
   Number of Shares of Common Stock Beneficially Owned Prior to this
Offering(1)(2)(3)
   Maximum Number of Shares to be Sold Pursuant to this
Prospectus(1)(2)(3)
Advent Convertible Master (Cayman) LP (ACM)   12,561   12,561   3,130,077   3,130,077
Alpha U.S. Sub Fund 4 LLC (ACM)   497   497   123,847   123,847
Banc of America Securities LLC   6,250   6,250   1,557,438   1,557,438
BNP Paribas Equity Strategies SNC   4,876   4,876   1,367,799   1,215,051
BP Amoco PLC Master Trust   394   394   98,181   98,181
Context Convertible Arbitrage Offshore, LTD   2,475   2,475   616,746   616,746
CooperNeff Convertible Strategies (Cayman) Master Fund, L.P.   5,402   5,402   1,346,125   1,346,125
Geode U.S. Convertible Arbitrage Fund   3,000   3,000   747,570   747,570
HFR Arbitrage Fund (ACM)   682   682   169,948   169,948
Hotel Union & Hotel Industry of Hawaii Pension Plan   143   143   35,634   35,634
Institutional Benchmarks Master Fund Ltd.   853   853   212,559   212,559
Jefferies & Company, Inc.   3   3   748   748
Lyxor (ACM)   1,345   1,345   335,161   335,161
Lyxor/Convertible Arbitrage Fund Limited   324   324   80,738   80,738
McMahan Securities Co. L.P.   500   500   124,595   124,595
Singlehedge U.S. Convertible Arbitrage Fund   1,081   1,081   269,374   269,374
Sphinx Convertible Arb Fund SPC   148   148   36,880   36,880
SSI Blended Market Neutral L.P.   211   211   52,579   52,579
SSI Hedged Convertible Market Neutral L.P.   235   235   58,560   58,560
Sturgeon Limited   604   604   150,511   150,511
Tag Associates (ACM)   104   104   25,916   25,916
Viacom Inc. Pension Plan Master Trust   13   13   3,239   3,239
Victory Convertible Fund   500   500   124,595   124,595
(1)
Pursuant to Rule 416(a) of the Securities Act of 1933, as amended, this registration statement also covers any additional securities that may be offered or issued to prevent dilution resulting from stock splits, stock dividends or similar transactions.

(2)
We prepared this table based on the information supplied to us on or before April 5, 2004 by the selling securityholders named in this table. Except as otherwise indicated, the number of shares owned represents less than 1% of our outstanding shares as of March 31, 2004. The inclusion of any shares in this table does not constitute an admission of beneficial ownership for the named selling securityholder.

(3)
Assumes conversion of all the holder's notes at a conversion price of approximately $4.013 per share of common stock. However, this conversion price will be subject to adjustment as described under "Description of Notes—Conversion of Notes" in the prospectus. As a result, the amount of common stock issuable upon conversion of the convertible notes may increase or decrease in the future.

        Investing in the convertible notes involves risks that are described in the "Risk Factors" section beginning on page 4 of the prospectus.

        Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of the prospectus or this prospectus supplement. Any representation to the contrary is a criminal offense.

        The date of this prospectus supplement is April 5, 2004