The purpose of the study was to assess the relative importance of risk factors for surgical site infections (SSI) following total hip and total knee prostheses in The Netherlands. In the period 1996-99 63 hospitals in The Netherlands registered SSI after 36,629 orthopedic operations. Total hip and total knee prostheses were analyzed in detail. The results of our study showed that a long preoperative stay was a risk factor for deep SSIs after both procedures. A dirty or contaminated wound and a serious systemic condition were risk factors for deep SSIs after total hip prostheses. If post-discharge surveillance was carried out, more SSIs were found, for total knee prostheses more than twice as many. Independent risk factors for SSIs after total hip prostheses were a contaminated/dirty wound and for total knee prostheses a short operation duration. The authors conclude that surveillance of surgical site infections following total hip and total knee prostheses revealed different risk factors for (deep) SSIs.