There is an increased risk of colorectal cancer among first degree relatives of affected men and women which is greater among relatives of young index patients. The high risk in some families can be explained by Mendelian patterns of inheritance and some syndromes associated with colorectal cancer have been recognized. Syndrome recognition with an accurate knowledge of the natural history of diseases caused by a single gene effect can offer opportunities for exploration of some of the mechanisms of carcinogenesis as well as enable more accurate predictions of diagnosis in susceptible individuals and in pregnancy. Recent progress with familial adenomatous polyposis illustrates some of the opportunities for prevention of colorectal cancer which may arise with syndrome recognition in the future.