Hereditary colorectal cancer results from specific genetic alterations. The causative genes for familial adenomatous polyposis, juvenile polyposis, Peutz-Jeghers syndrome, and hereditary nonpolyposis colorectal cancer have been cloned and characterized within the past decade. Genetic testing has therefore become more widely used to confirm the clinical diagnosis of each of those syndromes, to provide adequate surveillance, to allow screening of at-risk family members, and to help the surgeon in surgical decision making. The aim of this review is to analyze the importance of genetic testing in view of the clinical and surgical management of those gene-carriers individuals, and to discuss how should the surgeon integrate genetic testing in the evaluation of such patients.