Cancer is a hereditary disease at the level of an individual cell and its daughter cells. The tumor genotype causing the tumor phenotype is now quite well known in colorectal cancer and allows, among others, to perform pathology examination at the molecular level. A distinct topic addresses individual predisposition to colorectal cancer. Its molecular nature is well know in the relatively rare cases, about 5-10% of colorectal cancers, where such a predisposition is major, and is transmitted in families of affected subjects following a hereditary, mendelian mode of inheritance. Specifically, two types of hereditary adenomatous tumors, polyposis and hereditary nonpolyposis colorectal cancer, may benefit from genetic analysis in order to target cancer prevention. New genetic tests will probably develop in the coming years, allowing for the analysis of more modest, and less clearly hereditary individual risks.