Background. Today, only carcinoma of the bronchus kills more people than colorectal cancer (CRC). However, CRC is both preventable and curable. In Norway, projects aiming to detect adenomas and early cancers by the screening of a population aged about 60 years employing sigmoidoscopy have been discussed. Materials and methods: In this study, a mathematical model was used to estimate the cost-effectiveness of a screening programme for colorectal polyps followed by polypectomy. A once-only sigmoidoscopy at age 60 followed by coloscopy in selected risk groups was suggested. Data from the English-language literature, the National Cancer Registry of Norway, and Statistics Norway were included. Norwegian cost data from the National Health Administration were also used. Costs of screening and those related to earlier diagnosis, and savings on health care and averted loss in production due to prevented CRCs were calculated. Results: The basic cost per patient invited and screened (70% compliance) in the suggested programme was estimated at pound 81.7 and pound 116.7, respectively When gains due to prevented CRCs were included, the figures became pound 34.5 and pound 49.2. The cost per life-year saved was calculated as pound 2,889. This strongly indicates that screening for the early detection and prevention of CRC is one of the most cost-effective programmes in cancer. Conclusions. CRC screening according to the suggested programme appears to be cost-effective. Clear evidence that screening can reduce mortality from CRC should convince health-care policy makers that the time has come to encourage screening for colorectal cancer.