OMB APPROVAL OMB Number: 3235-0116 Expires: March 31, 2003 Estimated average burden hours per response: 8 Form 6-K SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Report of Foreign Private Issuer Pursuant to Rule 13a-16 or 15d-16 of the Securities Exchange Act of 1934 For the month of June, 2005 CONVERIUM HOLDING AG ------------------------------------------ (Translation of registrant's name into English) Baarerstrasse 8 CH-6300 Zug Switzerland ------------------------------------------------------- (Address of principal executive offices) Indicate by check mark whether the registrant files or will file annual reports under cover Form 20-F or Form 40-F. Form 20-F X Form 40-F ------- ------- Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934. Yes No X ------- ------- If "Yes" is marked, indicate the file number assigned to the registrant in connection with Rule 12g3-2(b): 82- Not Applicable Dodge & Cox acquires 5.04% of Converium's registered shares Disclosure of shareholdings pursuant to Art. 20 SESTA Zug, Switzerland - June 22, 2005 - Converium Holding Ltd has been notified that Dodge & Cox, 555 California Street, 40th Fl., San Francisco, CA 94104, U.S.A., has acquired 7,389,852 registered shares with voting rights. This corresponds to 5.04% of Converium's registered share capital. These shares are held and managed in the Dodge & Cox International Stock Fund. Dodge & Cox provides investment management to institutions and individuals through separately managed portfolios and mutual funds. Contacts: Zuzana Drozd Head of Investor Relations zuzana.drozd@converium.com Phone +41 (0) 1 639 91 20 Fax +41 (0) 1 639 71 20 Esther Gerster Head of Public Relations esther.gerster@converium.com Phone +41 (0) 1 639 90 22 Fax +41 (0) 1 639 70 22 www.converium.com 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, thereunto duly authorized. CONVERIUM HOLDING AG By: /s/ Terry Clarke Name: Terry Clarke Title: CEO By: /s/ Christian Felderer Name: Christian Felderer Title: General Legal Counsel Date: June 23, 2005