Incidence and prevalence of inflammatory bowel disease in Japan: nationwide epidemiological survey during the year 1991.

The aim of this nationwide study was to determine the recent incidence and prevalence of inflammatory bowel disease, i.e., Crohn's disease (CD) and ulcerative colitis (UC), in Japan. We mailed out a preliminary examination sheet with diagnostic criteria, asking about the presence of patients with inflammatory bowel disease, to all hospitals in Japan that have more than 200 beds for general use. The rate of reply was 60.93%. A total of 4243 patients with CD were reported. The incidence per 100 000 population per annum was 0.51 (0.71 in males, 0.32 in females). The prevalence per 100 000 population per annum was 5.85 (7.94 in males, 3.83 in females). Peak age at onset was 20-24 years in males and 15-19 years in females. A total of 12559 cases of UC were reported. The incidence per 100 000 population per annum was 1.95 (2.23 in males, 1.68 in females). The prevalence per 100 000 population per annum was 18.12 (18.70 in males, 18.17 in females). Peak age at onset was 20-24 years in males and 25-29 years in females.