To determine whether risk factors of ulcerative colitis among Japanese are the same as those observed in other countries, we conducted a case-control study in Japan in 1988–90. Patients selected for the study were receiving financial aid for treatment of the disease; an equal number of population-based controls matched by age and sex were selected. Smoking decreased the risk of the disease (odds ratio = 0.30; 95% confidence interval, 0.16–0.56), and stopping smoking increased the risk (odds ratio compared with those who had never smoked = 1.44; 95% confidence interval, 0.73–2.85). In those who drank alcoholic beverages ≥ 5 days a week, disease development was less likely than in others (odds ratio = 0.49; 95% confidence interval, 0.30–0.81). In addition, difficulties in human relations at work, a family history of asthma, a medical history of surgical procedures, and personality traits such as nervousness, anxiety, and obsessive behavior were also considered risk factors. Although some findings are similar to those in former studies, a few findings are different: surgical procedures, occupational status, and a family history of the disease. To clarify whether the differences are consistent will require other case-control studies.