Summary A large scale survey was conducted to examine risk factors for surgical site infections (SSIs) among Japanese patients undergoing gastrointestinal surgery. The purposes of the study were: (i) to investigate age as a risk factor for SSIs in gastrointestinal surgery; and (ii) to examine the differences in risk factors for SSIs between laparoscopic cholecystectomy and open cholecystectomy. Surveillance data were prospectively collected from 20 participating hospitals in Japan between July 2003 and November 2007. SSIs were identified by use of the Centers for Disease Control and Prevention criteria. SSIs were identified in 1471 of 12 015 available cases, with an overall incidence of 12.2%. In the final logistic regression model, age was a risk factor in open cholecystectomy, gastrectomy and appendicectomy. Length of operation was a risk factor for SSIs for six surgical procedures, and wound class and drain use were also risk factors in most procedures. When comparing laparoscopic surgery against open procedure, use of silk sutures was a risk factor for SSIs in laparoscopic cholecystectomy. Drain use, wound class, operation duration, male gender and age were additional risk factors for SSIs in open cholecystectomy. In summary, patient age is a significant predictor for SSIs in some gastrointestinal procedures, although risk factors for SSIs in laparoscopic procedures appear quite different from those in open procedures.