BACKGROUND & AIMS: The colectomy rate in ulcerative colitis (UC) is related to morbidity and to treatment decisions made during disease course. The aims of this study were to determine the colectomy risk in UC in the first decade after diagnosis and to identify factors that may influence the choice of surgical treatment. METHODS: In 1991-1993, 781 UC patients from 9 centers located in 7 countries in northern and southern Europe and in Israel were included in a prospective inception cohort study. After 10 years of follow-up, 617 patients had complete medical records, 73 had died, and 91 had been lost to follow-up. RESULTS: There were no significant differences in age, sex, or disease extent at diagnosis between patients followed for 10 years and those lost to follow-up. The 10-year cumulative risk of colectomy was 8.7%: 10.4% in the northern and 3.9% in the southern European centers (P < .001). Colectomy was more likely in extensive colitis than in proctitis, with an adjusted hazard ratio (HR) of 4.1 (95% CI: 2.0-8.4). Compared with the southern centers, the adjusted HR was 2.7 (95% CI: 1.3-5.6) for The Netherlands and Norway together and 8.2 (95% CI: 3.6-18.6) for Denmark. Age at diagnosis, sex, and smoking status at diagnosis had no statistically significant influence on colectomy rates. CONCLUSIONS: The colectomy rate was found to be lower than that in previous publications, but there was a difference between northern and southern Europe. Colectomy was associated with extensive colitis, but the geographic variations could not be explained.