BACKGROUND AND AIMS: In order to study the course of Behqets colitis, we eva1uated the response to medical and surgical treatment of the patients with Behqets colitis. METHODS: We analyzed 54 patients who were treated under the diagnosis of Behqets colitis for ten years between June, 1986 and December, 1996 at Seoul National University Hospital. Follow-up durations, symptoms, involved organs, involved sites, types of therapy, the response to therapy and response duration were evaluated. RESULTS: With 29 male and 25 female patients, the male to female ratio was 1.16:1, and the mean age was 34 years. Post-therapy follow-up durations ranged from 3 months to 25 years with the mean being 59 months (+56 months). Most colonic lesions were found in the ileocecal area. 91% were found in the ileocecal rea, 28% in the ascending colon, 15% in the transverse colon, 13% in the descending colon, 13% in the sigmoid colon, and 2% in the rectum. Wben colonic lesions were classified according to location and multiplicity, localized solitaiy lesions accounted for 44%, diffuse multiple lesions were 31%, and localized multiple lesions were 24%. Among those who underwent meclical therapy initially, 74.4% had remission or improvement. In average it took 4 weeks to have a response and 31 months before recurrence occurred. After medical treatment 23% of the patients underwent surgical treatment due to intractablility. 44% of all patients underwent operation, total operation nwnber was 42. Causes of operation were as follows; int6stinal perforation 33%, uncertain diagnosis 26%, intractable abdominal pain 19%, intestinal fistula 12%, and intestinal obstruction 10%. Operation incidence rate was 15/100 person-year and the 5-year cumulative operation rate was 47%. Those who underwent multiple operations were 22% of all patients and 50% of operation cases. Operation rates of diffuse multiple lesions, localized multiple lesions, and localized solitary lesions were 29%, 31%, and 63%. Reoperation rates were 80%, 75%, and 33% each. CONCLUSIONS: Behqet's colitis is a chronic recurrent disease. When medical therapy was effective, the response occurred within 8 weeks. Five-year cumulative operation rate was 47%. Re-operations were more frequent in diffuse multiple lesions, and explorative operations for confirmative diagnosis were more frequent in localized solitary lesions. Operations due to intestinal perforation made up 33% of all operations, so when the patients with Behcet's colitis were aggravated, we should consider the possibility of intestina1 perforation.