Colorectal cancer is the second commonest cause of cancer death. In a majority of cases it is preceded by a precancerous lesion called an adenoma (polyp). Detection and removal of adenomas at colonoscopy has been shown to reduce the death rate from colorectal cancer. However, despite meticulous examination there is a "miss rate" for adenomas at colonoscopy which ranges from 66-25% in back-to-back colonoscopy studies. The nature of the polyps which as well as being pedunculated (cherry like) can be flat or depressed making them difficult to see, which may contribute to the "miss rate".