Congenital heart disease has long been recognized in children with Down's syndrome, but little is known about the manifestations of clinical heart disease in adults with this condition. Therefore, 131 adults with Down's syndrome were examined. Clinical heart disease was considered to be present when an abnormally split S2, systolic click, at least grade 3/6 systolic precordial murmur, or any diastolic precordial murmur was heard. Using these criteria, 38 patients had clinical heart disease and 93 did not. To confirm and evaluate the auscultatory findings, echocardiograms were recorded in 37 of the patients. Comparison between patients without clinical heart disease and those with clinical heart disease showed that neither age (39 +/- 11 vs 40 +/- 12 years, respectively) nor gender (60% vs 66% men, respectively) differed significantly. Eleven had clinical and echocardiographic findings consistent with atrial or ventricular septal defect. Findings consistent with aortic regurgitation were identified in 8, and 18 had mitral valve prolapse. These results suggest that in addition to atrial and ventricular septal defect (which have a well recognized association with Down's syndrome), 2 specific, usually asymptomatic, and heretofore unanticipated valvular cardiac abnormalities may be associated with Down's syndrome.