==============================================================================

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                 SCHEDULE 13D/A

                  Under the Securities Exchange Act of 1934
                                (Amendment No. 4)

                               Agere Systems Inc.
           ---------------------------------------------------------
                                (Name of Issuer)

               Class A Common Stock, par value $0.01 per share
                         (Title of Class of Securities)

                                   00845V 10 0
                -------------------------------------------------
                                 (CUSIP Number)
       ------------------------------------------------------------------

                                Scott A. Arenare
                      Managing Director and General Counsel
                               Warburg Pincus LLC
                              466 Lexington Avenue
                            New York, New York 10017
                                 (212) 878-0600
       ------------------------------------------------------------------
            (Name, Address and Telephone Number of Person Authorized
                     to Receive Notices and Communications)

                                 With a copy to:
                              Andrew R. Brownstein
                         Wachtell, Lipton, Rosen & Katz
                               51 West 52nd Street
                            New York, New York 10019
                                 (212) 403-1000


                                 April 29, 2003
       ------------------------------------------------------------------
             (Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report
the acquisition that is the subject of this Schedule 13D, and is filing this
schedule because of ss.ss. 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the
following box: [ ].

                                Page 1 of 8 Pages

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   1          NAME OF REPORTING PERSON
              I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS
                      Warburg Pincus Private Equity VIII, L.P.
                      I.R.S. IDENTIFICATION NO. 13-4161869
--------------------------------------------------------------------------------
   2          CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
                                                                     (a)  [X]
                                                                     (b)  [ ]
--------------------------------------------------------------------------------
   3          SEC USE ONLY                                       [ ]
--------------------------------------------------------------------------------
   4          SOURCE OF FUNDS
                    WC
--------------------------------------------------------------------------------
   5          CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
              PURSUANT TO ITEMS 2(d) OR 2(e)                              [ ]
--------------------------------------------------------------------------------
   6          CITIZENSHIP OR PLACE OF ORGANIZATION
                    DELAWARE
--------------------------------------------------------------------------------
    NUMBER OF               7.  SOLE VOTING POWER
                                     -0-
     SHARES
                    ------------------------------------------------------------
  BENEFICIALLY
                            8.  SHARED VOTING POWER
    OWNED BY                         45,290,212*

      EACH          ------------------------------------------------------------
                            9.  SOLE DISPOSITIVE POWER
   REPORTING                         -0-

  PERSON WITH       ------------------------------------------------------------
                           10.  SHARED DISPOSITIVE POWER
                                     45,290,212*

--------------------------------------------------------------------------------
     11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
                    45,290,212*
--------------------------------------------------------------------------------
     12       CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN
              SHARES                                                       [ ]
--------------------------------------------------------------------------------
     13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
                    6.0%**
--------------------------------------------------------------------------------
     14       TYPE OF REPORTING PERSON
                    PN
--------------------------------------------------------------------------------


-------------------------
* Assumes the full conversion of the Convertible Subordinated Notes beneficially
owned by the Investors in accordance with their terms.
**Represents the percentage of Class A Common Stock beneficially owned by WP
VIII as of April 29, 2003 assuming full conversion of the Convertible
Subordinated Notes beneficially owned by the Investors in accordance with their
terms.  Based on the same assumption, as of April 29, 2003, WP VIII beneficially
owned 2.7% of the outstanding Class A Common Stock and Class B Common Stock,
taken as a whole.




--------------------------------------------------------------------------------
   1          NAME OF REPORTING PERSON
              I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS
                      Warburg Pincus & Co.
                      I.R.S. IDENTIFICATION NO. 13-6358475
--------------------------------------------------------------------------------
   2          CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
                                                                     (a)  [X]
                                                                     (b)  [ ]
--------------------------------------------------------------------------------
   3          SEC USE ONLY                                       [ ]
--------------------------------------------------------------------------------
   4          SOURCE OF FUNDS
                    WC
--------------------------------------------------------------------------------
   5          CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
              PURSUANT TO ITEMS 2(d) OR 2(e)                              [ ]
--------------------------------------------------------------------------------
   6          CITIZENSHIP OR PLACE OF ORGANIZATION
                    NEW YORK
--------------------------------------------------------------------------------
    NUMBER OF               7.  SOLE VOTING POWER
                                     -0-
     SHARES
                    ------------------------------------------------------------
  BENEFICIALLY
                            8.  SHARED VOTING POWER
    OWNED BY                         45,290,212*

      EACH          ------------------------------------------------------------
                            9.  SOLE DISPOSITIVE POWER
   REPORTING                         -0-

  PERSON WITH       ------------------------------------------------------------
                           10.  SHARED DISPOSITIVE POWER
                                     45,290,212*

--------------------------------------------------------------------------------
     11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
                    45,290,212*
--------------------------------------------------------------------------------
     12       CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN
              SHARES                                                       [ ]
--------------------------------------------------------------------------------
     13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
                    6.0%**
--------------------------------------------------------------------------------
     14       TYPE OF REPORTING PERSON
                    PN
--------------------------------------------------------------------------------


-------------------------
* Assumes the full conversion of the Convertible Subordinated Notes beneficially
owned by the Investors in accordance with their terms.
**Represents the percentage of Class A Common Stock beneficially owned by WP
as of April 29, 2003 assuming full conversion of the Convertible Subordinated
Notes beneficially owned by the Investors in accordance with their terms.  Based
on the same assumption, as of April 29, 2003, WP beneficially owned 2.7% of the
outstanding Class A Common Stock and Class B Common Stock, taken as a whole.

                                      -3-




--------------------------------------------------------------------------------
   1          NAME OF REPORTING PERSON
              I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS
                      Warburg Pincus LLC
                      I.R.S. IDENTIFICATION NO. 13-3536050
--------------------------------------------------------------------------------
   2          CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
                                                                     (a)  [X]
                                                                     (b)  [ ]
--------------------------------------------------------------------------------
   3          SEC USE ONLY                                       [ ]
--------------------------------------------------------------------------------
   4          SOURCE OF FUNDS
                    WC
--------------------------------------------------------------------------------
   5          CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
              PURSUANT TO ITEMS 2(d) OR 2(e)                              [ ]
--------------------------------------------------------------------------------
   6          CITIZENSHIP OR PLACE OF ORGANIZATION
                    NEW YORK
--------------------------------------------------------------------------------
    NUMBER OF               7.  SOLE VOTING POWER
                                     -0-
     SHARES
                    ------------------------------------------------------------
  BENEFICIALLY
                            8.  SHARED VOTING POWER
    OWNED BY                         45,290,212*

      EACH          ------------------------------------------------------------
                            9.  SOLE DISPOSITIVE POWER
   REPORTING                         -0-

  PERSON WITH       ------------------------------------------------------------
                           10.  SHARED DISPOSITIVE POWER
                                     45,290,212*

--------------------------------------------------------------------------------
     11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
                    45,290,212*
--------------------------------------------------------------------------------
     12       CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN
              SHARES                                                       [ ]
--------------------------------------------------------------------------------
     13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
                    6.0%**
--------------------------------------------------------------------------------
     14       TYPE OF REPORTING PERSON
                    OO
--------------------------------------------------------------------------------

-------------------------
* Assumes the full conversion of the Convertible Subordinated Notes beneficially
owned by the Investors in accordance with their terms.
**Represents the percentage of Class A Common Stock beneficially owned by WP LLC
as of April 29, 2003 assuming full conversion of the Convertible Subordinated
Notes beneficially owned by the Investors in accordance with their terms.  Based
on the same assumption, as of April 29, 2003, WP LLC beneficially owned 2.7% of
the outstanding Class A Common Stock and Class B Common Stock, taken as a whole.


                                      -4-




                               AMENDMENT NO. 4 TO

                                  SCHEDULE 13D

            Reference is made to the statement on Schedule 13D filed on June 21,
2002, Amendment No. 1 thereto filed July 29, 2002, Amendment No. 2 thereto filed
October 17, 2002 and Amendment No. 3 thereto filed April 8, 2003 (as so amended,
the "Schedule 13D") on behalf of Warburg Pincus Private Equity VIII, L.P., a
limited partnership organized under the laws of Delaware ("WP VIII"), Warburg
Pincus & Co., a general partnership organized under the laws of New York ("WP"),
and Warburg Pincus LLC, a limited liability company organized under the laws of
New York ("WP LLC", and together with WP VIII and WP, the "Reporting Persons").
All capitalized terms used without definition herein have the meanings ascribed
thereto in the Schedule 13D. This Amendment No. 4 to the Schedule 13D amends the
Schedule 13D as follows.

ITEM 5.     INTEREST IN SECURITIES OF THE ISSUER.

Item 5 of the Schedule 13D is amended as follows:

(a)  The Reporting Persons beneficially own shares of Class A Common Stock by
     virtue of the Investors' beneficial ownership of shares of Class A Common
     Stock and of the Issuer's 6.5% Convertible Subordinated Notes due 2009 (the
     "Convertible Subordinated Notes"), which are convertible at the option of
     the holder into 330.75 shares of Class A Common Stock per $1,000 principal
     amount of Convertible Subordinated Notes, subject to adjustment in certain
     circumstances. As of April 29, 2003, the Reporting Persons beneficially
     owned an aggregate of 45,290,212 shares of Class A Common Stock,
     representing 33,650,000 shares of Class A Common Stock beneficially owned
     by the Investors and 11,640,212 shares of Class A Common Stock that may be
     acquired by the Investors upon full conversion of the Convertible
     Subordinated Notes beneficially owned by the Investors. Of the aggregate of
     45,290,212 shares of Class A Common Stock beneficially owned by WP and WP
     LLC, approximately 1,399,468 shares represent shares of Class A Common
     Stock beneficially owned by WPNPE VIII I, WPNPE VIII II and WPGPE VIII. By
     reason of WP's and WP LLC's respective relationships with the Investors,
     under Rule 13d-3 of the Exchange Act, WP and WP LLC may be deemed to
     beneficially own all of the shares of Class A Common Stock that are
     beneficially owned by the Investors.

     Assuming full conversion of the Convertible Subordinated Notes beneficially
     owned by the Investors, as of April 29, 2003, the 45,290,212 shares of
     Class A Common Stock beneficially owned by each Reporting Person
     represented approximately 6.0% of the outstanding shares of Class A Common
     Stock, and 2.7% of the Issuer's outstanding shares of Class A Common Stock
     and Class B Common Stock, par value $0.01 per share (the "Class B Common
     Stock"), taken as a whole, in each case, after giving effect to the
     issuance of the Class A Common Stock upon full conversion of the
     Convertible Subordinated Notes beneficially owned by the Investors (based
     on 744,288,076 shares of Class A Common Stock and 907,995,677 shares of
     Class B Common Stock outstanding as of January 31, 2003, as set forth in
     the Issuer's Form 10-Q for the quarterly period ended December 31, 2002).


                                      -5-



(b)  As described in paragraph (a) above, the Group Members have beneficial
     ownership over an aggregate of 45,290,212 shares of Class A Common Stock.
     Of this aggregate of 45,290,212 shares of Class A Common Stock, 33,650,000
     shares are represented by the shares of Class A Common Stock beneficially
     owned by the Investors and 11,640,212 are represented by shares of Class A
     Common Stock that are issuable to the Investors upon full conversion of the
     Convertible Subordinated Notes beneficially owned by the Investors. Each of
     the Investors shares voting power and dispositive power over the shares of
     Class A Common Stock that such Investor beneficially owns with WP LLC and
     WP.

(c)  The Investors disposed of Convertible Subordinated Notes with an aggregate
     principal amount of $44,800,000 in brokered transactions as described
     below:



                                                                               

          Date          Aggregate Principal     Price (% of Principal         Gross Proceeds (not including
                              Amount                 Amount)                     accrued interest)
      ------------      -------------------     ---------------------         ------------------------------

        4/17/03            $10,000,000                94.13%                          $9,412,500
        4/21/03             $2,000,000                96.50%                          $1,930,000
        4/22/03             $2,000,000                96.63%                          $1,932,500
        4/23/03             $4,100,000                97.10%                          $3,981,002
        4/29/03            $26,700,000                99.76%                         $26,636,988



      Except as described herein, since the date of Amendment No. 3 to the
      Schedule 13D, there have been no transactions in shares of Class A Common
      Stock effected by the Reporting Persons or, to the best of their
      knowledge, by any of the persons set forth on Schedule I.

(d)  Except as set forth in this Item 5, no person other than each respective
     record owner referred to herein of the shares of Class A Common Stock is
     known to have the right to receive or the power to direct the receipt of
     dividends from, or the proceeds from the sale of, such shares of Class A
     Common Stock.

(e)  Not applicable.

                                      -6-




                                   SIGNATURES

            After reasonable inquiry and to the best of our knowledge and
belief, the undersigned certify that the information set forth in this statement
is true, complete and correct.

Dated:  April 29, 2003


                               WARBURG PINCUS PRIVATE EQUITY VIII, L.P.

                               By: Warburg Pincus & Co.,
                                   General Partner

                                  By: /s/ Scott A. Arenare
                                      ----------------------------------------
                                        Name:  Scott A. Arenare
                                        Title: Partner


                               WARBURG PINCUS & CO.

                               By: /s/ Scott A. Arenare
                                  --------------------------------------------
                                  Name:  Scott A. Arenare
                                  Title: Partner


                               WARBURG PINCUS LLC

                               By: /s/ Scott A. Arenare
                                  --------------------------------------------
                                  Name:  Scott A. Arenare
                                  Title: Member


                               WARBURG PINCUS NETHERLANDS PRIVATE EQUITY VIII
                                  C.V. I

                               By:  Warburg Pincus & Co.,
                                    General Partner

                                  By: /s/ Scott A. Arenare
                                     -----------------------------------------
                                        Name:  Scott A. Arenare
                                        Title: Partner


                                      -7-




                               WARBURG PINCUS NETHERLANDS PRIVATE EQUITY VIII
                                     C.V. II

                               By:  Warburg Pincus & Co.,
                                    General Partner

                                  By: /s/ Scott A. Arenare
                                     -----------------------------------------
                                        Name:  Scott A. Arenare
                                        Title: Partner


                               WARBURG PINCUS GERMANY PRIVATE EQUITY VIII KG

                               By:  Warburg Pincus & Co.,
                                    General Partner

                                  By: /s/ Scott A. Arenare
                                     -----------------------------------------
                                        Name:  Scott A. Arenare
                                        Title: Partner