The aim of this study was to estimate temporal trends in the incidence of surgical site infection (SSI) using a large SSI surveillance network in southeast France from 1995 to 2003. Data were analysed from 187 surgical wards that had participated in the network for at least two years. The change in SSI rate over time was modelled using a hierarchical logistic regression model with patients clustered within surgical wards. Of the 200 207 patients selected, 3786 (1.9%) had an SSI. The nine-year trend in SSI rate estimated by an odds ratio of 0.95 (95% confidence interval 0.93-0.97) was interpreted as a 5% decrease in SSI rate per year. This decrease was constant over the study period and was observed for almost all of the different types of surgical operations (orthopaedic, gastrointestinal, urology, etc). Overall SSI rates were reduced by 45% over a period of nine years. This trend was maintained even when taking into account the heterogeneity of the surgical wards and the diversity of patient demographics over time. From this, the 5% decrease per year can be reasonably interpreted as a result of preventive measures taken by surgical wards to reduce SSIs.