Screening and early diagnosis of colorectal cancer Colorectal cancer, major health problem in industrialised countries, fulfils the conditions required for mass screening. Data from controlled studies indicate that it is possible to reduce colorectal cancer mortality at a population level using faecal occult blood testing. Population-based studies rely on biennial testing in subjects between 50 and 74 and total colonoscopy in case of positive test. The colorectal cancer mortality decrease in this case varies between 15 and 28% in the general population, 33 and 39% among participants to screening. In order to decrease significantly colorectal cancer mortality compliance has to be over 50%. On the basis of available data, the European Commission recommended to organise colorectal cancer screening in the EU. Epidemiological studies allow us to define subjects at high risk for colorectal cancer. Colonoscopy screening is recommended in first degree relatives of patients with colorectal cancer diagnosed before 60 or 65 or with two affected first-degree relatives, in subjects with an extended ulcerative colitis or Crohn disease or with a personal history of large bowel cancer or large adenoma.