The hospital incidence of Crohn's disease in the Helsinki metropolitan area during 1975-1985 was studied retrospectively. The resident population in this urban, well-defined district was 790,000 in the year 1985. During this period 193 new patients suffering from Crohn's disease were diagnosed. The annual incidence increased three times from 1/100,000 to 3/100,000, while the annual mean incidence was 2,3/100,000. The age-specific incidence was highest in the age-groups 15-24 with no sex difference. After the initial rapid increase the incidence of Crohn's disease in the Helsinki metropolitan area has stabilized on the level 3/100,000. These figures are similar to those reported from other Scandinavian and Western countries.