Lower gastrointestinal bleeding (LGIB) in children has many different etiologies and is a serious problem that warrants careful diagnostic work-up. Materials and Methods164 colonoscopies were done during one year for determining the etiologies of LGIB in children who was referred to Children's Medical Center Hospital. Analyses of results were based on age, sex, etiology and clinical presentations. Results Of 164 colonoscopies, 34.7% of LGBI were due to polyps which was the most common etiology. Lymphoid nodular hyperplasia (LNH) had a prevalence of 22.5%; in 15.8% of patients, colonoscopic findings were normal. The peak age group of polyps was 4–6 yr; for LNH, itwas 1 yr. Conclusions LNH is more common than polyps in patients presenting with LGIB younger than 3 yrs. In older children, however, polyps are the major cause. Therefore, the diagnostic approach and the need for colonoscopy are different in these two age groups.