Colonoscopy is a procedure that enables an examiner (usually a gastroenterologist) to evaluate the appearance of the inside of the colon (large bowel). This is accomplished by inserting a long flexible tube (the colonoscope) that is about the thickness of a finger into the anus and then advancing the colonoscope slowly into the rectum and through the colon. The tip of the colonoscope has a light and a video camera. The inner colon lining can be directly visualized in images transmitted from the camera to a television monitor. This traditional method of examining the colon is called optical colonoscopy or, more commonly, just colonoscopy.