Objective.Surgical site infection (SSI) is one of the most common healthcare-associated infections (HAIs). This study aims to assess factors associated with SSI after colorectal surgery in Japan, using a Japanese national database for HAIs.Design.A retrospective nationwide surveillance-based study.Setting.Japanese healthcare facilities.Methods.Data on colon and rectal surgeries performed from 2008 through 2010 were extracted from a national monitoring system for healthcare-associated infections, the Japan Nosocomial Infections Surveillance (JANIS). Factors associated with SSI after colon and rectal surgery were assessed using multivariate logistic regression.Results.The cumulative incidence of SSI for colon and rectal surgery was 15.0% (6,691 of 44,751) and 17.8% (3,230 of 18,187), respectively. Traditional risk factors included in the National Nosocomial Infections Surveillance (NNIS) modified risk index were significant in predicting SSI in the final model for both colon and rectal surgery. Among the additional variables routinely collected in JANIS were factors independently associated with the development of SSI, such as male sex (adjusted odds ratio [aOR], 1.20 [95% confidence interval (CI), 1.14–1.27]), ileostomy or colostomy placement (aOR, 1.13 [95% CI, 1.04–1.21]), emergency operation (aOR, 1.40 [95% CI, 1.29–1.52]), and multiple procedures (aOR, 1.22 [95% CI, 1.13–1.33]) for colon surgery as well as male sex (aOR, 1.43 [95% CI, 1.31–1.55]), ileostomy or colostomy placement (aOR, 1,63 [95% CI, 1.51–1.79]), and emergency operation (aOR, 1.43 [95% CI, 1.20–1.72]) for rectal surgery.Conclusions.For colorectal operations, inclusion of additional variables routinely collected in JANIS can more accurately predict SSI risk than can the NNIS risk index alone.Infect Control Hosp Epidemiol 2014;35(6):660–666