Incidence of Crohn's disease in four counties in southeastern Norway, 1990-93. A prospective population-based study. The Inflammatory Bowel South-Eastern Norway (IBSEN) Study Group of Gastroenterologists.

Background: Standardized criteria for Crohn's disease (CD) have only recently been developed, and prospective community-based incidence studies have been performed only during the past 3 decades. Geographic variations in incidence may therefore be due to differences in study design.

Methods: From 1 January 1990 to 31 December 1993 all new cases of CD in four counties in southeastern Norway were prospectively registered.

Results: A total of 225 new cases yielded an annual incidence of 5.8/10(5), with the highest incidence in mixed rural-urban areas. A peak of 11.2/10(5) in the annual incidence was found for the age group 15 to 24 years, with no significant differences in the overall annual incidence by gender. An average duration of 6 months of disease before diagnosis was unchanged during the 4 years. About half of the patients had isolated colonic disease, and one-quarter had isolated small-bowel disease.

Conclusions: This study confirms the high incidence figures for Scandinavia, with a particularly high incidence in mixed rural-urban areas. Ileocolonoscopy improves the accuracy of the diagnosis and of the determination of disease extent, which may have therapeutic implications for the treatment and follow-up of patients.