In Hokkaido, 131 patients with Crohn's disease have been confirmed during the past 8 years from Jan. 1978 to Dec. 1985. Epidemiological aspects of this disease entity were investigated in accordance with official inquiry protocol in the present study. The results were as follows; 1) Composition of patients with Crohn's disease was 84 cases (64.1%) and 47 cases (35.9%) for males and females, respectively. The average age of the onset was 24.9(14?55) years in males and 28.2(13?66) years in females, which resulted in a mean of 25.9(13?66) years of the total cases. 2) The geographical locations of this desease was 129 cases and 2 cases in and out of Hokkaido, respectively. The distribution of patients was 52 cases (40.3%) in Ishikari district, which was most numerous, and was followed by 19 cases (14.7%), 12 cases (9.3%), 11 cases (8.5%), 8 cases (6.2%), 7 cases (5.4%) and 20 cases (15.5%), in Kamikawa, Sorachi, Iburi, Oshima, Abashiri and other districts, respectively. 3) The rate of incidence (per year per 100,000 populations) appeared to be gradually increasing year by year and was 0.04 in 1978 to 0.58 in 1985. The average of the last 8 years was 0.38 in males and 0.21 in females, resulting in 0.29 for both. 4) The occurrence by place of residence was 2.7 (per 100,000 populations) and 1.3, in urban and rural dwellers, respectively. This disease is more prevalent in the densely populated areas. 5) Ages of diagnosis was 54 cases (41.2%), 39 cases (29.8%) and 19 cases (14.5%) in 20s, 10s and 30s year, respectively. 6) The results in clinical statistics regarding initial symptoms and signs at onset, site of involvement, laboratory findings, x-ray and endoscopic findings, histological features, complications and treatments were not different from those in the other reports in Japan. The present observations indicate obviously that patients with Crohn's disease have increased recently also in Hokkaido, especially among younger generations, which exerted a serious influence on sociomedical aspects. Further investigations as to the pathogenesis and treatment must be carried out immediately.