OBJECTIVES: Cumulative 10-yr relapse rates in ulcerative colitis (UC) of 70% to almost 100% have been reported in regional studies. The aim of this study was to determine the relapse rate in UC in a European population-based cohort 10 yr after diagnosis and to identify factors that may influence the risk of relapse. METHODS: From 1991 to 1993, 771 patients with UC from seven European countries and Israel were prospectively included in a population-based inception cohort and followed for 10 yr. A relapse was defined as an increase in UC-related symptoms leading to changes in medical treatment or surgery. The cumulative relapse rate, time to first relapse, and number of relapses in the follow-up period were recorded and possible causative factors were investigated. RESULTS: The cumulative relapse rate of patients with at least one relapse was 0.67 (95% CI 0.63-0.71). The time to first relapse showed a greater hazard ratio (HR) (1.2, CI 1.0-1.5) for women and for patients with a high level of education (1.4, CI 1.1-1.8). The number of relapses decreased with age, and current smokers had a lower relapse rate (0.8, CI 0.6-0.9) than nonsmokers. The relapse rate in women was 1.2 (CI 1.1-1.3) times higher than in men. An inverse relation was found between the time to the first relapse and the total number of relapses. CONCLUSION: In 67% of patients, there was at least one relapse. Smoking status, level of education, and possibly female gender were found to influence the risk of relapse.