The removal of adenomatous polyps of the large bowel reduces mortality from colorectal cancer (CRC). Faecal occult blood testing only reveals 20.40% of polyps. The flexible rectosigmoidoscope explores less than half of the large bowel. Its use should always be coupled with faecal occult blood testing which, if positive, requires a total colonoscopy. The sensitivity of double-contrast barium enema for the search of polyps is 35%. Colonoscopy does not reach the caecum in about 10% of cases. It misses 15-20% of polyps with diameter <10 mm and about 6% of polyps with diameter >10 mm. Virtual colonoscopy has substantially the same sensitivity as optical colonoscopy for polyps > or =7 mm in diameter.