Although restorative proctocolectomy is recognized as a standard procedure for ulcerative colitis, infectious complications after surgery cannot be disregarded. The aim of this study was to define predictors of surgical site infection (SSI) in urgent/emergent surgery for ulcerative colitis. We performed prospective SSI surveillance for 90 consecutive patients. Possible risk factors were analyzed by logistic regression analyses. Incidences of incisional SSI (i-SSI) and organ/space SSI were 31.1% and 6.9%, respectively, and increased significantly with higher wound class (P < 0.01). Multivariate analysis showed wound class ≥3 as an independent risk factor for i-SSI. In univariate analysis, although the mucous fistula procedure was a risk factor for i-SSI (odds ratio, 3.45; P < 0.01), Hartmann procedure also represented a risk factor for o-SSI (odds ratio, 12.8; P < 0.01). Urgent restorative proctocolectomy for patients without high wound class and emergent total colectomy with mucous fistula for patients with high wound class appear to represent feasible options.