A colonoscopy involves the insertion of a lighted flexible tube, called a colonoscope, into the rectum. The tube is inserted so that the lining of the colon is visualized. Any area of the lining that appears abnormal may be biopsied; that is, a piece of tissue may be removed for analysis. In addition, growths of the colon, called polyps, may be removed (polypectomy) by the use of an electrified wire, called a snare.

A colonoscopy is generally a safe procedure but carries several risks that include, but are not limited to, the following: bleeding from biopsy or polypectomy; perforation or puncture of the colon which would likely require a surgical operation to repair; and, contact colitis; that is, irritation of the lining of the colon from contact with the colonoscope. Serious complications of colonoscopy, such as perforation or bleeding, may require hospitalization, blood transfusions, or surgery.