Colonoscopy is a procedure that involves a doctor inserting a thin, flexible, tube-shaped, lighted instrument through the rectum to examine the inside of the large intestine (colon). Sometimes doctors use colonoscopy to look for the cause of a patient's symptoms (diagnostic colonoscopy). Another use of colonoscopy is to look for polyps (growths that can become cancer) or cancer (screening colonoscopy). During colonoscopy, it is possible to take samples of the colon (biopsies), to remove polyps or small cancers, and to stop bleeding from abnormalities within the colon. Complications of colonoscopy include perforation (a hole in the wall of the colon), bleeding at the site of a biopsy or polyp removal, postpolypectomy pain due to damage of the colon wall during polyp removal, and diverticulitis. Diverticulitis is an infection that can occur in people who have diverticulosis. In diverticulosis, small pouches are in the wall of the colon. Colonoscopy is thought to be a relatively safe procedure. However, much of the information on complications has come from studies or referral centers and might not reflect what actually happens in the general community.