Four members of a family, thirteen subjects of which developed cancer for three consecutive generations were surgically treated in our Unit for colon cancer. It is well known to day that adenocarcinoma of the colon, as well as of other organs, has been proved to occur in certain families by a dominant trait, in the absence of any precancerous lesions. Due to this and because none of our patients has had any of the above mentioned lesions and because their tumors developed in the colon de novo, we have to accept that there is a hereditary predisposition in the development of familial cancer generally, which holds for our patients too. Because of a very high incidence of cancer, close follow-up of these families is recommended, that must start early and completed by chromosome and immunobiologic studies for all first, second and third dergee relatives.