Reduction of surgical site infection. Retrospective evaluation of a surgical infection prevention program consisting of the gradual introduction of specific infection prevention methods and a surveillance system identifying and reporting on potentially preventable surgical site infections as defined by the omission of a preventive method. A university tertiary referral medical center. The sequential introduction of infection prevention elements in the bundle resulted in a fluctuating rate of potentially preventable surgical site infections simultaneously with a slow, gradual reduction of the clean wound SSI rate. Change in a complex, multidisciplinary environment such as an inpatient surgical unit happens gradually and requires focused attention and input from all involved professionals.