Patients presenting with rectal bleeding were prospectively categorized according to the pattern of their presentation into those with outlet bleeding (n = 115), suspicious bleeding (n = 59), hemorrhage (n = 27), and occult bleeding (n = 68). All patients underwent colonoscopy and this was complete in 94 percent. There were 34 patients with carcinoma and 69 with adenomas greater than 1 cm diameter. The percentage of neoplasms proximal to the splenic flexure was 1 percent in outlet bleeding, 24 percent with suspicious bleeding, 75 percent with hemorrhage, and 73 percent with occult bleeding. Barium enema was available in 78 patients and was falsely positive for neoplasms in 21 percent and falsely negative in 45 percent. Colonoscopy is the investigation of choice in patients with suspicious, occult, or severe rectal bleeding. Bleeding of a typical outlet pattern may be investigated by flexible sigmoidoscopy.