Backgroud/Aims: The frequency of different etiologies of lower gastrointestinal bleeding varies by a number of factors including patient age, the severity of bleeding evaluated, the diagnostic method, and the institution. There were few reports on the clinical analysis of lower gastrointestinal bleeding in Korea. Therefore, this study was conducted to evaluate the frequency of various etiologies, diagnostic methods, and the management of patients with lower gastrointestinal bleeding. Methods: 474 patients with lower gastrointestinal bleeding who were admitted to Samsung Medical Center from September 1994 to April 1998 were reviewed. The inclusion criteria were as follows: 1) age at least 15 years, and 2) patients whose bleeding was attributed to a lesion distal to the ligament of Treitz. The age and sex distribution, etiology, diagnostic methods, treatment, and transfusion were checked. Results: 474 patients (261 males and 213 females) met the inclusion criteria. The average age of the patients was 51 years old. The etiologies of bleeding were as follows: colorectal cancer, 43%; anorectal disease, 32%; inflammatory bowel disease, 6.6%; ischemic colitis, 5%; miscellaneous, 6%; and unknown, 7.4%. Colonoscopy was the most commonly employed diagnostic modality and was used in 245 (52%) patients of the study group. Other tests included sigmoidoscopy in 136 (29%), barium enema in 90 (19%), small bowel radiography in 24, radionuclide bleeding scans in 8, and mesenteric angiography in 7. Patients who improved with conservative and medical treatment were 29%, and 71% required surgery. Patients who required a transfusion were 37%. 139 patients (68.8%) with diagnosed malignant neoplasm received a transfusion. Conclusions: The incidence of lower gastrointestinal bleeding was high in old age. Colorectal cancer was the most common cause and required surgery. Colonoscopy was a valuable diagnostic tool for the evaluation of lower gastrointestinal bleeding. (Korean J Gastrointest Endosc 19: 911∼917, 1999)