We identified patients aged 25 to 74 with a bacteriologically confirmed first episode of gastroenteritis, from a recent study that examined the association between acid suppressing drugs and the development of gastroenteritis.⁵ We excluded all patients with a history of irritable bowel syndrome, cancer, or alcoholism. We sampled a comparison cohort from the source population from which patients with gastroenteritis had been ascertained. We applied the same eligibility criteria as were used for the ascertainment of the gastroenteritis cohort, but the subjects had to be free of gastroenteritis at the start of follow up. We then followed up both cohorts during 1 year until the earliest occurrence of one of the following end points: diagnosis of irritable bowel syndrome, cancer, alcohol misuse, or death. To confirm diagnoses, we sent a questionnaire to the doctors of all patients with irritable bowel syndrome in the gastroenteritis cohort and a 10% random sample (n=216) to the doctors of patients with irritable bowel syndrome in the general population. We used Poisson regression to calculate incidence, relative risk, and 95% confidence intervals of irritable bowel syndrome associated with gastroenteritis. The general population cohort was used as the reference group, and the estimates were adjusted for age, sex, and body mass index.