A family with autosomal dominant cancer was first reported one century ago. The heredi­tary nature of some forms of colorectal cancer was confirmed less than 10 years ago by the detection of mutations associated with genetic predispositions to mendelian colorectal can­cer. The paper presents several hereditary types of colorectal carcinoma, as well as their phe­notypic and genetic characteristics, which allow for differential diagnosis of various syndromes. The role of molecular genetic technology in familial and population genetics is stressed. The paper describes the molecular genetic technique used at the Laboratory of mole­cular genetics Institute of Pathology Medical Faculty Ljubljana for the identification of fami­lies with hereditary non-polyposis colorectal cancer in the Slovene population.