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%).