The onset and course of ulcerative colitis diagnosed in 38 children at or before 10 years of age were reviewed. The mean age at onset was 5.9 years. A family history of inflammatory bowel disease was present in 24% of patients, and 13% had a history of cow milk allergy in infancy. Initially, by radiologic or colonoscopic studies, 71% had total colonic disease, 13% had left-sided colitis, and 6% had proctitis; extensive examination was not performed in 4 patients. Four patients (11%) presented with severe colitis, 14 (37%) with moderate colitis, and 20 (53%) with mild colitis. The most frequent symptoms were abdominal pain (94%), diarrhea (84%), and rectal bleeding (84%). Between 2 and 10 years after diagnosis, 89% of children had total colonic disease and 11% had left-sided disease. All four patients with severe disease at onset responded to medical therapy with one having a colectomy 15 years later with pathology consistent with Crohn's disease. Of those with moderate disease, half had infrequent moderate recurrences and half had intermittent mild disease. One patient had colectomy at 21 years for intractable disease. Of the 20 with mild disease, 16 continued to have intermittent mild recurrences, 1 had chronic mild disease, 2 had moderate recurrent disease, and 1 has remained asymptomatic for 5 years. Psychiatric disturbances requiring therapy were identified in 5 (13%) children. Results are encouraging: after the first 2 years of illness, two thirds of the children have had subsequent mild colitis with infrequent relapses and three quarters consider their life to be of good quality.