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 July, 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 Zurich Cantonal Bank increases its holding of Converium's registered shares to 5.001% and reduces again to below 5% Disclosure of shareholdings pursuant to Art. 20 SESTA Zug, Switzerland - July 7, 2005 - Converium Holding Ltd has been notified that Zurich Cantonal Bank, Tessinerplatz 7, 8002 Zurich, Switzerland, adjusted its holding of registered shares of Converium Holding Ltd, Zug on June 29, 2005 to 5.001% and on June 30, 2005 to below 5%. Zurich Cantonal Bank states that the above-mentioned stock of shares is a pure trading position, which is generated during the normal course of its derivative business. Contacts: Zuzana Drozd Head of Investor Relations zuzana.drozd@converium.com -------------------------- Phone +41 (0) 44 639 91 20 Fax +41 (0) 44 639 71 20 Esther Gerster Head of Public Relations esther.gerster@converium.com ---------------------------- Phone +41 (0) 44 639 90 22 Fax +41 (0) 44 639 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: July 8, 2005