EXHIBIT 21 SUBSIDIARIES OF PENTON MEDIA INC. 1. Donohue Meehan Publishing Company, an Illinois corporation. 2. Internet World Media, Inc., a Delaware corporation, and its wholly-owned subsidiaries: A. Penton Business Media London Limited, a United Kingdom corporation; B. One, Inc., a Colorado corporation; C. Boardwatch Magazine, Incorporated, a Colorado corporation; D. Penton Internet, Inc., a Delaware corporation; E. Penton Media Australia Pty. Limited, an Australian corporation; and F. Penton Media Ireland Limited, an Ireland corporation. 3. New Hope International Limited, a United Kingdom corporation. 4. Penton Business Media (Holdings) London Limited, a United Kingdom corporation, and its wholly-owned subsidiaries: A. Equity Information Exchange Limited, a United Kingdom corporation; B. Penton Media (Europe) Limited, a United Kingdom corporation, and its wholly-owned subsidiary: a. Hillgate Communications Limited, a United Kingdom corporation, and its wholly-owned subsidiary: (1) Hillgate Custom Publishing, a United Kingdom corporation; C. Service Exhibitions Limited, a United Kingdom corporation; D. Penton Media International Limited, a United Kingdom corporation, and its 60% ownership subsidiary: a. Penton Media Spain S.A., a Spain corporation; and E. Lightspeed Integrated Media Limited, a United Kingdom corporation. 5. Stardust.com, a California corporation. 6. Streaming Media, Inc., a California corporation. 7. Duke Investments, Inc, a Colorado corporation, and its wholly-owned subsidiary: A. Duke Communications International, Inc., a Colorado corporation, and its wholly owned subsidiary: a. Duke Communications Europe Limited, a United Kingdom corporation. 8. PTS Delaware, Inc., a Delaware corporation. 9. Tech Conferences, Inc., a Connecticut corporation. 10. Healthwell.com, Inc., a Delaware corporation. 11. ComMunic GmbH Kongresse-Messen Seminare, a Germany corporation. 12. Penton Media, S. de R.L. de C.V., a Mexico corporation. 13. Penton Media Asia Limited, a Hong Kong corporation. 14. Penton Media France (SAS), a France corporation. 15. Service Management Publication Limited, a United Kingdom Corporation.