Colorectal cancer is a collective term for a heterogeneous group of diseases. In a large proportion of cases, the condition is attributable to genetic predisposition. Those directly involved in the treatment of patients with cancer of the large bowel are confronted to an increasing degree with the genetic aspects of the disease. In familial and hereditary forms of the disorder periodic screening of the close relatives of the patients can in principle prevent disease and death from colorectal cancer. Presymptomatic diagnosis by means of DNA technology is now possible in many cases of familial...