A colonoscopy (koe-lun-OSS-kuh-pee) is a test that uses a long, flexible instrument to examine the inside of the rectum and colon. This hollow device has a sensor at the end that relays images to a viewing screen. Doctors may recommend the exam if you've had unexplained rectal bleeding, changes in bowel habits, or unusual abdominal symptoms. It may also be used to confirm the presence of polyps or tumors, or simply to monitor patients who've had colon cancer or polyps. A day or two before your exam, you'll be instructed to take laxatives to cleanse the bowel, and may be restricted to a liquid diet. During the procedure, the scope is advanced to the junction of the small intestine, or as far as circumstances allow. If needed, a smaller instrument can be passed inside the scope to take a sample of tissue, or remove benign growths on the colon called polyps. Most colonoscopies are done on an outpatient basis, and take less than an hour. You'll usually be sedated, experience little discomfort, and afterwards, may not recall the procedure. One of the major benefits of colonoscopy is the ability to locate and remove most polyps without major surgery. Removing polyps can help prevent colon cancer. To find out more about colonoscopy, consult a doctor.