The incidence of Crohn's disease (CD) and ulcerative colitis (UC) in children in western Norway was estimated in a prospective epidemiological study during the years 1984 and 1985. The total population in the area was 807,000 and the child population was 198,570 (1984). There were 27 new cases of chronic inflammatory bowel disease (IBD) in children aged 15 years or less, 10 new cases of CD, and 17 of UC. The mean annual incidence of CD in the child population was 2.5/100,000/year, whereas the incidence of UC in the child population was 4.3/100,000/year. Nearly all the children had abdominal symptoms. In this study, we found an incidence of CD in children that is the highest hitherto reported, to our knowledge. To the contrary, the incidence of UC was considerably lower than previously reported from northern Europe.