[Screening coloscopy: when and how?].

Screening colonoscopy aims at a reduction of colorectal cancer mortality. The efficacy is undetermined due to lack of controlled trials. However, screening colonoscopy is generally accepted in asymptomatic patient with a considerably increased risk for carcinoma in particular in case of familial adenomatous polyposis coli, hereditary nonpolypous colorectal cancer syndrome and adenomas detected by sigmoidoscopy. A positive cost/benefit ratio can also be expected in first-degree relatives of patients with familial sporadic colorectal carcinoma. To date the efficacy of colonoscopic surveillance of patients with extensive ulcerative colitis remains undetermined in spite of an increased risk of cancer in the long-term course. In people with an average risk for colorectal cancer the probability of a development of carcinoma might be reduced by about 45% by once-only sigmoidoscopy performed at the age of 50-60 years. Further reduction can theoretically be expected from routine colonoscopy. However, before a general recommendation can be given, the efficacy must be proved in a randomised controlled trial.