Part of the NIDEP study was to determine the prevalence of surgical site infections in the surgical departments of 72 representatively selected hospitals. Four physicians, trained and validated in detecting nosocomial infections, carried out the surveillance, based on the CDC criteria for nosocomial infections. The prevalence of surgical site infections was 1.34% for all surgical patients (n = 5377) and 2.13% for all operated patients (n = 3383). Lower rates were found in patients with a low ASA score, clean wounds, and an average duration of the operation. Most surgical site infections were noted after amputations (7.2%), operations on colon or rectum (4.1%), and appendectomies (3.8%).