Flexible sigmoidoscopy is a safe, effective test that may be delivered feasibly on a large scale for mass colorectal cancer screening. Flexible sigmoidoscopy is 67% to 80% as sensitive as colonoscopy in a screening population, but is probably 10 to 20 times safer than colonoscopy in terms of complications. Several national guidelines recommend combining flexible sigmoidoscopy with fecal occult blood tests. There is limited evidence to support this practice, and the added benefit to an existing flexible sigmoidoscopy screening program although real, may be marginal. In the future, it is likely that flexible sigmoidoscopy screening among patients aged 50 to 65 will be supplemented with total colonic screening, using molecular-based fecal tests or virtual colonoscopy, after age 65.