Background:Surveillance of surgical site infections (SSI) provides data upon which interventions to improve patient safety can be based. In Thailand, however, SSI surveillance has not yet been standardized.Objectives:To develop a standardized SSI surveillance system and to monitor SSI rates after introduction of such a system.Methods:We conducted a prospective study among 17,752 patients who underwent surgery in ten hospitals in Thailand from April 2004 to May 2005. The SSI rates were computed and benchmarked with the US rates, reported in terms of standardized infection ratio (SIR). We estimated the incidence rate ratio of surgical site infections by comparing the incidence in the last study period with the incidence in the first study period.Results:The study included 17,869 operations and identified 248 SSIs, yielding an SSI rate of 1.4 infections/100 operations and a corresponding SIR of 0.6 (95% confidence interval [CI] = 0.5–0.7). During the study period the overall SSI rate decreased from 1.8 infections/100 operations to 1.2 infections/100 operations, yielding an incidence rate ratio of 0.65 (95% CI = 0.47–0.89).Conclusion:Our study highlighted that a standardized SSI surveillance in a developing country can be initiated through a network and may be followed by a decrease in SSI rates.