Endoscopic removal of premalignant adenomas from the distal bowels of the entire population, 3 to 5-yearly from age 50, is advocated in the US as a feasible method of reducing colorectal cancer mortality rates. In the UK, a single flexible sigmoidoscopy (FS) is regarded as a more cost-effective option. Although more acceptable than colonoscopy, FS and polypectomy are expensive and invasive procedures carrying a small risk of serious harm. We believe that, before implementing mass screening, precise estimates are required of the magnitude of the reduction in mortality and costs (financial, physical and emotional). Several randomized trials, including a large British study, are currently evaluating these aspects.