The Danish Hereditary Nonpolyposis Colorectal Cancer (HNPCC) Register is a national resource that registers families with hereditary colorectal cancer. HNPCC is the most common type of hereditary colorectal cancer and carries an increased risk of other tumor types. Genetic diagnostics has identified 88 unique mutations in 164 Danish families delineated as Lynch syndrome families. Predictive genetic diagnostics enables the identification of high risk individuals, who are offered participation in surveillance programmes that effectively reduce morbidity and mortality in colorectal cancer.