In order to examine the presentation and course of Crohn's disease (CD) versus those of ulcerative colitis (UC) in children < or = 10 years of age, a retrospective review of children < or = 10 years old with inflammatory bowel disease singled out 40 patients and compared their findings with those of 38 children with UC. The mean age at onset was 7.5 years for CD, as compared with 5.9 years for UC. A family history of inflammatory bowel disease was present in 13 patients (32%). Abdominal pain (97%), diarrhea (78%), and weight loss (88%) were the major initial complaints, with growth retardation present in 12 (30%) children. At onset, four children had diffuse small-bowel disease, nine had terminal ileal disease, 15 had ileocolitis, and 12 had colitis; at the end of the study two had diffuse small-bowel disease, four had terminal ileal disease, 25 had ileocolitis, and seven had colitis. Extra-intestinal manifestations increased with duration of disease. Although the number of recurrences did not differ greatly between groups, those with ileocolitis and colitis needed longer steroid therapy and more days in hospital than did those with only small-bowel disease. Operation was required in 42.5% of children with CD, as compared with 5% of those with UC, with six CD children (35%) requiring later reoperation for recurrent disease or fistula and abscess. Two children died from causes unrelated to their disease (gastric volvulus, carcinoma of the breast).(ABSTRACT TRUNCATED AT 250 WORDS)