The incidence and prevalence of chronic inflammatory bowel disease (IBD) in children was established during 1984 and 1985 in a prospective study in Sweden. The patients with IBD were classified as having ulcerative colitis (UC), Crohn's disease (CD), probable Crohn's disease (PCD), and indeterminate colitis (IC) according to defined histopathologic, endoscopic, and radiologic criteria. The study covered 1.51 million children less than 16 years of age (93% of all children in Sweden). The incidence of IBD was 5.0 and 4.5 and the prevalence was 17.6 and 18.2 per 100,000 children during the 2 years, respectively. The mean prevalence of UC was 7.5 per 100,000 and of CD + PCD was 6.2 per 100,000. The prevalence of IC was 4.2 per 100,000, which corresponds to 23% of the children with IBD.