Background: Colonoscopy is used for both diagnostic as well as therapeutic purposes in patients with lower GI symptoms. The aim of this study was to assess the clinical manifestations and to determine the colonoscopic findings of children with lower GI symptoms attending a pediatric hospital in Tehran.Materials and Methods: During a 5-year period (1996-2001), all children less than 16 years of age, who had undergone colonoscopy in the Gastroenterology Department of the Children's Hospital Medical Center in Tehran (Iran), were studied in respect to presenting symptoms, colonoscopy and pathologic findings, and the size, number and site of polyps if they were present.Results: Among the 694 children (431 boys, 263 girls) less than 16 years of age who entered this study, 49.4%, who underwent colonoscopy, were aged between 1 and 5 years.Hematochezia, rectal prolapsed, diarrhea, constipation, abdominal pain, fever, growth retardation, Clubbing, history of ulcerative colitis and polyps were present in 93.2%, 5.9%, 2.7%, 0.6%, 3.7%, 2.6%, 1.4%, 0.6%, 1.4%, 0.7% of the patients, respectively. Polyps, nodular lymphoid hyperplasia (NLH), granularity ulceration (suggestive for ulcerative colitis), suggestive for crohn's disease, mucosal edema, fragility, ulcer, solitary rectal ulcer, cobblestone appearance, vascular disorders, fissure, fistula and anal tags were present in 34.6%, 16.7%, 15.1%, 0.9%, 1.9%, 0.6%, 2.4%, 3.7%, 0.4%, 0.6%, 3%, 0.6% of the patients, respectively; 23.1% of the children had normal colonoscopy findings. Among the 240 cases found to have polyps on colonoscopy, 209, 18, 7, 4, 2 cases were reported as juvenile polyps, hamartoma, hyperplastic, lymphoid and necrotic in type, respectively. Of the 232 patients with polyps, 197 had a solitary polyp, 22 had 2 to 4 polyps, and 13 had more than 5 polyps. In respect to site, polyps were more frequent in the rectum, recto sigmoid region, left colon, diffuse, and right colon in decreasing order of occurrence.Conclusions: Colonoscopy is performed more frequently in children with hematochezia and rectal prolapsed. Polyps, NLH and ulcerative colitis were the most frequent findings in the colonoscopies performed.