To assess the feasibility of a prospective incidence study of inflammatory bowel disease (IBD), the registration methods and incidence figures during 1990 were evaluated. The study was a collaboration between 14 hospitals in an area of close to one million inhabitants. Common diagnostic criteria for ulcerative colitis (UC), Crohn's disease (CD) and indeterminate colitis (IND) were established prior to the start of the study. There was an overall incidence rate for IBD of 19.3 per 10(5) inhabitants, with 10.6 for UC, 5.1 for CD and 3.6 for IND. The age-specific incidence rates showed a peak between 25 and 34 years for UC and between 15 and 25 for CD. There was a male predominance for UC and a female preponderance for CD. These results are comparable with the previous registrations in western and northern areas of Norway.