The Cardiovascular Health Study is a population-based longitudinal study of 5,201 adults aged 65 years and older. Prevalences of myocardial infarction, angina pectoris, congestive heart failure, peripheral artery disease, stroke, and transient ischemic attack were ascertained between June 1989 and May 1990 in participants recruited from Forsyth County, North Carolina; Washington County, Maryland; Sacramento County, California; and Pittsburgh, Pennsylvania. A medical history was taken to obtain self-reports of prevalent disease. For all participants, use of nitrates was ascertained to document angina, electrocardiograms were used to document prevalent myocardial infarction, and ankle-arm blood pressure studies were used to document peripheral artery disease. Self-reports of disease that were not confirmed by examination findings were further investigated by examination of medical records. Reported disease that was confirmed by examination findings or by medical records was classified as "definite." Disease that was documented by examination, but not reported by the participant, was classified as "unreported." The prevalence rates of definite myocardial infarction and angina were 11% and 15%, respectively, among men aged 65-69 years, 18% and 17% among men aged 80-84 years, 4% and 8% among women aged 65-69 years, and 3% and 13% among women aged 80-84 years. Twenty-three percent of men and 38% of women with electrocardiographic evidence of myocardial infarction did not report it. These results suggest that prevalent disease estimates based only on self-report may underestimate the prevalence of cardiovascular diseases in older Americans.