A colonoscopy is an examination of the lining of the bowel (the colon or large intestine) with a long, flexible instrument called a colonoscope.

It is passed into the rectum (back passage) and around the colon. On the end of it is a tiny camera that sends pictures to a video screen. Your doctor or nurse uses the pictures to look for anything unusual.

S/he may also take small tissue samples (biopsies) from the bowel lining during the test. These will be sent to the laboratory to be looked at under a microscope.