Increasingly, researchers and health specialists are obtaining information on chronic illnesses from self-reports. This study validates self-reports of two major health conditions, hypertension and diabetes, based on a recent survey in Taiwan (SEBAS 2000). These data, based on a large, nationally representative sample of respondents aged 54 and older, include both self-reported health information and a physical examination. Average blood pressure readings, laboratory measures of glycosylated hemoglobin, and information on whether the respondent was taking medication for hypertension or diabetes are used to validate respondents' reports of high blood pressure and diabetes. The resulting comparisons reveal that self-reports vastly underestimate the prevalence of hypertension, but yield a reasonably accurate estimate of the prevalence of diabetes. Significant correlates of the accuracy of the self-reports include age, education, time of the most recent health exam, and cognitive function.