EXHIBIT 15.1 LETTER REGARDING UNAUDITED INTERIM FINANCIAL INFORMATION



Board of Directors and Shareholders

STERIS Corporation



We are aware of the incorporation by reference in the following Registration Statements and related Prospectuses of our report dated
January 24, 2005 relating to the unaudited consolidated interim financial statements of STERIS Corporation and subsidiaries that are included in its Form 10-Q for the quarter ended December 31, 2004:



|                   |  |                                                                                                                                                                                                                  
|------------------ |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|RegistrationNumber |  | Description                                                                                                                                                                                                      
|333-101308         |  | Form S-8 Registration Statement  STERIS Corporation 2002 Stock Option Plan                                                                                                                                      
|                   | 
|333-91302          |  | Form S-8 Registration Statement  Nonqualified Stock Option Agreement between STERIS Corporation and Mark D. McGinley                                                                                            
|                   | 
|333-63774          |  | Form S-8 Registration Statement  Nonqualified Stock Option Agreement between STERIS Corporation and Peter A. Burke                                                                                              
|                   | 
|333-63770          |  | Form S-8 Registration Statement  Nonqualified Stock Option Agreement between STERIS Corporation and Charles L. Immel and Restricted Shares Agreement between STERIS Corporation and
Charles L. Immel            
|                   | 
|333-40082          |  | Form S-8 Registration Statement  Nonqualified Stock Option Agreement between STERIS Corporation and Laurie Brlas and the Nonqualified Stock Option Agreement between STERIS Corporation
and David L. Crandall   
|                   | 
|333-40058          |  | Form S-8 Registration Statement  Nonqualified Stock Option Agreement between STERIS Corporation and Les C. Vinney                                                                                               
|                   | 
|333-65155          |  | Form S-8 Registration Statement  STERIS Corporation 1998 Long-Term Incentive Compensation Plan                                                                                                                  
|                   | 
|333-55839          |  | Form S-8 Registration Statement  Nonqualified Stock Option Agreement between STERIS Corporation and John Masefield and the Nonqualified Stock Option Agreement between STERIS Corporation
and Thomas J. DeAngelo
|                   | 
|333-32005          |  | Form S-8 Registration Statement  STERIS Corporation 1997 Stock Option Plan                                                                                                                                      
|                   | 
|333-06529          |  | Form S-3 Registration Statement  STERIS Corporation                                                                                                                                                             
|                   | 
|333-01610          |  | Post-effective Amendment to Form S-4 on Form S-8  STERIS Corporation                                                                                                                                            
|                   | 
|33-91444           |  | Form S-8 Registration Statement  STERIS Corporation 1994 Equity Compensation Plan                                                                                                                               
|                   | 
|33-91442           |  | Form S-8 Registration Statement  STERIS Corporation 1994 Nonemployee Directors Equity Compensation Plan                                                                                                         
|                   | 
|33-55976           |  | Form S-8 Registration Statement  STERIS Corporation 401(k) Plan                                                                                                                                                 
|                   | 
|33-55258           |  | Form S-8 Registration  STERIS Corporation Amended and Restated Non-Qualified Stock Option Plan                                                                                                                  



/s/ ERNST & YOUNG LLP




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|Cleveland, Ohio 
|February 8, 2005