From an incidence cohort diagnosed during 1962-1987 we identified all patients with onset of IBD before the age of 15 in order to describe the course and to compare course and prognosis with adult onset IBD. The mean incidence of IBD among children below 15 years was 2.2/10(5), 2.0 for ulcerative colitis (UC), and 0.2 for Crohns disease (CD). At diagnosis, UC children had more extensive disease compared to adults (p < 0.05). Abdominal pains were also more frequent. The cumulative colectomy probability was 6% after one year and 29% after 20 years, not different from adults. Regarding disease activity, it was found that 60-70% of UC patients were in remission in the first 10 years of disease, for CD about 50% were in remission. One UC patient developed carcinoma of the sigmoid colon. Time between onset and development of carcinoma was 12 years. For CD no differences in clinical appearance at diagnosis and course between children and adults were found. No deaths occurred among CD patients. Three CD patients were found to have severe growth retardation already at diagnosis. In conclusion, the incidence of IBD is low in childhood. At diagnosis children with UC have more widespread disease than adults. Children with CD do not differ in clinical presentation, course or prognosis compared to adult onset CD. However, growth retardation is a problem among CD patients.