The prevalence of cardiovascular disease in 453 subjects admitted consecutively to a state school for the retarded was 9%. All but three of the 41 subjects who had cardiovascular disease had congenital heart disease. The population contained 76 with Down's syndrome, 26% (20) of whom had heart disease. Of those who did not have Down's syndrome, 5.6% (21) had heart disease; this is approximately 25 times the rate in the normal population. There was a surprisingly high prevalence of diseases of the aortic valve or ascending aorta; 44% (18) of those with cardiovascular disease had this type.