The fecal occult blood test twobikes mentions is a common screening test that many doctors do during a regular physical. The benefit of a colonoscopy is that it can prevent colon cancer by removing pre-cancerous polyps. The FOBT cannot prevent cancer. If the result is positive, yu need a colonoscopy. If the result is negative, you could easily miss something important. If you're over 40, insist on the full monty.