There is now good evidence from case control studies and randomized controlled trials that screening average-risk subjects for colorectal cancer using faecal occult blood tests reduces mortality. There is limited data indicating that screening sigmoidoscopy can also achieve this. There is no evidence yet that screening by colonoscopy or double contrast barium enema can reduce mortality. Calculations of cost-effectiveness suggest that all of the above strategies should be economically worthwhile but there is no convincing evidence to suggest that one strategy is markedly more cost-effective than the others. Further data on several aspects of screening are required before any decisions are made on which form(s) of screening should be offered nationwide.