During a colonoscopy or a sigmoidoscopy, you lie on your side, and the doctor or nurse puts a thin tube with a camera into your anus (from behind). Then the doctor or nurse advances the tube into the rectum and colon. The camera sends pictures from inside your colon to a television screen. A colonoscopy allows the doctor to see the whole colon (shown in pink and green). A sigmoidoscopy allows the doctor to see only the last part of the colon (shown in green).
