A colonoscopy looks at the whole of the inside of the large bowel. A doctor or nurse (endoscopist) uses a flexible tube called a colonoscope. The tube has a small light and camera at one end. The endoscopist puts the tube into your back passage and passes it along the bowel. They can see pictures of the inside of your bowel on a TV monitor. Some of the reasons why you may need a colonoscopy are: to help find the cause of bowel symptoms, to look for early signs of bowel cancer as part of the national bowel cancer screening programmed, to look for early signs of bowel cancer if you are at high risk of developing bowel cancer, as part of your follow up after treatment for bowel cancer.