The purpose of this study was to determine the incidence of postinfectious irritable bowel syndrome (IBS) among community subjects with positive stool studies. This was a prospective cohort study whereby all individuals with stool-positive acute enteric infection (AEI) were recruited from 3 health regions in Ontario, Canada. Each person completed questionnaires regarding preinfectious bowel habit and their bowel habit 3 months postinfection. Manning and Rome I criteria were used to diagnose irritable bowel syndrome. Two hundred thirty-one patients participated. Forty had preexisting IBS and were excluded. Of the remaining 191 patients, 7 developed irritable bowel syndrome, for an incidence of 3.7% (95% confidence interval: 1.0-6.3%). Fever during AEI was the only identifiable risk factor for developing postinfectious IBS (odds ratio, 11.96; P = .02). The incidence of postinfectious IBS in community subjects is 3.7%. Fever during the AEI may be an important risk factor for this condition.