OBJECTIVE Colonic diverticular bleeding cases account for 30-40% of the lower gastrointestinal bleeding, among which, 3-5% appear to be massive bleeding. The purpose of this study was to evaluate the risk factors for colonic diverticular bleeding diagnosed by colonoscopic examination. METHODS Among the 1,003 patients, who were identified to have colonic diverticulosis including sleeding by diverticulitis and diverticular bleeding coding search, 216 patients had diverculosis, and they were divided into two groups: one with diverticular bleeding, and the other without bleeding. We evaluated the potential risk factors for diverticular bleeding, based on age, gender, location of diverticulum, comorbidities related to atherosclerosis, smoking, alcohol and medications, and compared them between both groups. RESULTS Among the 216 patients, we observed colonic diverticular bleeding in 35 patients (16.2%). The mean age of the bleeding group was significantly older than that of non-bleeding group. No difference was observed regarding gender ratio. Right colonic diverticula were common in both groups, but there were higher proportion of patients with bleeding in bilateral diverticuosis. Old age, bilateral diverticulosis, presence of atherosclerosis related diseases (hypertension, diabetes mellitus, ischemic heart disease, obesity), use of aspirin, NSAIDs and calcium channel blocker, increased the risk of bleeding. In a multivariate analysis, use of aspirin and bilateral diverticulosis were identified as independent risk factors for colonic diverticular bleeding. CONCLUSIONS Since the patients who took aspirin and/or had bilateral colonic diverticulosis increased the risk of bleeding from divertuculi. As such, caution and education of patients are required.