A colonoscopy is an internal examination of the colon (large intestine) and rectum, using a long, flexible, tubular instrument called a colonoscope.

The colonoscope has a small camera attached to a flexible tube.  Unlike sigmoidoscopy, which can only reach the lower third of the colon, colonoscopy examines the entire length of the colon.

The patient will lie on his left side with knees  drawn up toward the chest.  After administering a sedative and pain reliever, the colonoscope is inserted through the anus. It is gently moved into the beginning of the large bowel and sometimes into the lowest part of the small intestine. Air will be inserted through the scope to provide a better view. Suction may be used to remove fluid or stool. Tissue samples may be taken with tiny biopsy forceps inserted through the scope. Polyps may be removed with electrocautery snares, and photographs may be taken.