The Holt-Oram syndrome is an autosomal dominant disorder consisting of upper-extremity and cardiovascular anomalies. Three families are described that illustrate (1) the wide variability of expression of both the cardiovascular and upper-extremity abnormalities, (2) the use of syndrome identification and knowledge of the genetics of this disorder to identify other affected family members and to provide appropriate genetic counseling, and (3) the use of roentgenographic studies to identify affected persons.