The aim was to study determinants of postoperative bowel function after restorative proctocolectomy for ulcerative colitis. Medical records of patients who underwent proctocolectomy with ileal J pouch-anal anastomosis (IPAA) in two- or three-stage operations and whose status of defecation was known via a questionnaire were retrospectively reviewed. Bowel function, including stool frequency, stool consistency, and degree of nighttime soiling, was correlated with age at the time of surgery, time after ileostomy closure, mean resting anal pressure, longitudinal length of ileal J pouch, and duration of fecal diversion by using univariate and multivariate analyses. Stool frequency decreased significantly with time after ileostomy closure in both univariate and multivariate analyses. Stool frequency tended to be less in patients having a long J pouch, but the correlation was not significant (P = 0.071) in univariate analysis. Nighttime soiling ameliorated with time after ileostomy closure in multivariate, but not univariate, analysis. Deterioration of nighttime soiling was seen in patients whose duration for fecal diversion was long, both in univariate (P = 0.068) and multivariate (P = 0.052) analyses. Stool consistency was related to none of the five factors investigated. These results indicate that as the time after surgery increases, stool frequency decreases and nighttime soiling ameliorates. Delaying ileostomy closure because of anticipated postoperative incontinence does not significantly alter postoperative continence.