For the past two and half yeas, we have experienced 54 cases of urgent colonoscopy which was performed within 72 hours of the onset of anal bleeding. For its preparation, warm water enema was given to 46 patients, and cathartics were given to 8 patients. The following cases were included: 15 cases of drug induced colitis, 8 cases of colitis of unknown etiology, 5 cases of ischemic colitis, and 4 cases of infectious colitis. These cases usually demonstrated a rapid course and the origin of bleeding may well be obscure, when examined after bleeding has ceased. Urgent colonoscopy is, therefore, very useful. As a bleeding site was in most instances beyond the reach of a proctoscope, actually existing in the proximal colon, the colon must be examined as deep as possible until a bleeding point has been found. Urgent colonoscopy is very useful not only for an early diagnosis and treatment of acute colonic diseases, but also for solution of their pathophysiology. Urgent colonoscopy should be done more frequently, because it seems safe under cautious performance.