Surgical site infections (SSI) are a key target of nosocomial infection control policy. We evaluated the impact of a six-year surveillance system based on data from INCISO, a network of volunteer surgical wards from hospitals in Northern France. Each year surgical patients were enrolled consecutively and surveyed during their in- and out-hospital stay until 30 days following surgery. A standardised form was completed for each patient including SSI diagnosis according to standard criteria and several risk factors such as wound class, American Society of Anesthesiologists score, operation duration, elective/emergency, videoscopy and type of surgery. A dashboard was displayed at the end of each annual survey, so that participants could compare with other surgery adjusted for National Nosocomial Infections Surveillance system (NNIS) risk index and standardised incidence ratio (SIR). Over the six years, 3661 SSI were identified in 150 440 surgical patients (crude incidence: 2.4%) from 548 surgery wards. The crude SSI incidence decreased from 3.8 to 1.7% (P for trend <0.0001, relative reduction: -55%) and the NNIS-0 adjusted SSI incidence from 2.0 to 1% (P for trend <0.0001; relative reduction: -50%). An active surveillance system striving for benchmark through a network is an effective strategy to reduce SSI incidence. Sustaining control efforts have to be made to maintain low SSI level beyond the three primer years.