A review was made of 139 fiberoptic colonoscopies performed between 1975 and 1982 on 113 patients aged 1 month to 20 years. General anesthesia was used in four procedures. All others were done under sedation with meperidine (mean dose 2.9 mg/kg) and diazepam (mean dose 0.5 mg/kg). Indications were rectal bleeding in 52 patients; assessment and surveillance of known inflammatory bowel disease in 33 patients; and diagnostic evaluation of abdominal pain, diarrhea, and/or fever in 28 patients. The cecum was reached in 84% of diagnostic examinations. Comparison of findings on colonoscopy with barium enema in 75 patients showed agreement in 46, colonoscopic superiority in 25, and barium enema superiority in four. Bleeding sufficient to cause anemia was seen in 10/26 patients with polyps. Five minor complications and no major complications occurred. Flexible fiberoptic colonoscopy and polypectomy may be done usefully in childhood by physicians well versed and experienced with these procedures. Colonoscopy and biopsy changed the radiographic diagnosis from ulcerative colitis to Crohn's disease in several cases and indicated greater extent of colonic disease in several cases of ulcerative colitis and Crohn's disease. Colonoscopy is usually the most sensitive and accurate diagnostic tool for the evaluation of colonic disease, but barium enema and colonoscopy are complementary tests and barium enema should usually precede colonoscopy, with certain exceptions.