A two-year investigation of 517 families selected through a proband having a congenital heart disease suggests a higher frequency of familial congenital disease than has been reported before. Many previously undiagnosed parents and siblings of the probands were discovered by the simple method of listening to their hearts. Although figures of 3.4% affected sibs and 1.8% affected parents are presented, it is emphasized that these figures are used only to call attention to the high frequency of familial congenital heart diseases. The figures are not suggested as empiric risks because "congenital heart disease" is more appropriately a category of diseases than a discrete disease. An awareness that familial congenital heart diseases are perhaps not as uncommon as previously reported places a responsibility on the examining physician to other members of the family as well as to the patient.