OBJECTIVE To assess the structure and quality of surveillance activities and to validate outcome detection in the Swiss national surgical site infection (SSI) surveillance program. DESIGN Countrywide survey of SSI surveillance quality. SETTING 147 hospitals or hospital units with surgical activities in Switzerland. METHODS Site visits were conducted with on-site structured interviews and review of a random sample of 15 patient records per hospital: 10 from the entire data set and 5 from a subset of patients with originally reported infection. Process and structure were rated in 9 domains with a weighted overall validation score, and sensitivity, specificity, positive predictive value, and negative predictive value were calculated for the identification of SSI. RESULTS Of 50 possible points, the median validation score was 35.5 (range, 16.25-48.5). Public hospitals (P<.001), hospitals in the Italian-speaking region of Switzerland (P=.021), and hospitals with longer participation in the surveillance (P=.018) had higher scores than others. Domains that contributed most to lower scores were quality of chart review and quality of data extraction. Of 49 infections, 15 (30.6%) had been overlooked in a random sample of 1,110 patient records, accounting for a sensitivity of 69.4% (95% confidence interval [CI], 54.6%-81.7%), a specificity of 99.9% (95% CI, 99.5%-100%), a positive predictive value of 97.1% (95% CI, 85.1%-99.9%), and a negative predictive value of 98.6% (95% CI, 97.7%-99.2%). CONCLUSIONS Irrespective of a well-defined surveillance methodology, there is a wide variation of SSI surveillance quality. The quality of chart review and the accuracy of data collection are the main areas for improvement. Infect Control Hosp Epidemiol 2017;38:1172-1181.