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.