There is strong evidence that population screening can reduce mortality from colorectal cancer. Screening tests such as faecal occult blood test and flexible sigmoidoscopy are used to identify patients with an increased risk of cancer who would benefit from a full colon examination. There is indirect evidence that colonoscopy may be effective as a mass screening tool. Potential benefits of colonoscopy include the ability to visualize the entire colon and to detect and remove polyps, which could prevent cancers, and identify cancers if present anywhere in the colon. Issues related to the implementation of a colonoscopy screening programme are discussed.