The most frequent monogenic predisposition to CRC is hereditary non-polyposis colorectal cancer (HNPCC). Less frequent are syndromes with polyposis. In some families the occurrence of CRC indicates a familial risk of CRC without the diagnostic criteria for the above syndromes being fulfilled. In families where causative mutations are identified, predictive genetic testing is offered. When no mutation is identified in a family, the risk of individual members of the family is evaluated according to the family history. Individuals with a high risk of CRC are offered surveillance.