Objective: To obtain baseline-data of Surgical Site Infection (SSI) in our hospital, surveillance of SSI after general-gastrointestinal surgery and cardiac surgery was performed. Methods: All patients, who underwent general-gastrointestinal surgeries or cardiac surgeries in our hospital from January to December 1998., were registered and analyzed in this study. Surveillance of SSI was conducted following Center for Disease and Prevention (CDC) National Nosocomial Infections Surveillance System (NNIS) manual. Results: One thousand two hundred fifty four patients underwent the procedures. According to NNIS, SSI rates were analyzed by operative procedure and risk index category in surgical patient surveillance component. Total number of patients with SSI was 107, and total SSI ratewas 8.5%. Conclusion: The baseline-data of SSI in our hospital were obtained by this study. In comparison wit hNNIS, there were some differences in operative procedures in surgical category and duration cut point. P. aeruginosa seem to be an outbreak SSI pathogen of this year. In conclusion, NNIS can be applied to create infection control system in Keio Univ. Hospital with some modification.