To assess the relation of initial blood pressure (BP) taken in sitting, supine and standing positions to subsequent development of systemic hypertension, 1,564 men were followed for an average of 6.6 years. The men were participants in the Normative Aging Study, a longitudinal study of aging initiated in 1963 at the Veterans Administration Outpatient Clinic in Boston. After controlling for sitting levels of systolic BP and diastolic BP in a Cox regression model, supine systolic BP was found to be a significant predictor of subsequent hypertension. This effect of position was not solely a result of decreases in measurement error associated with using additional BP measurements. Although the physiologic mechanism for the observed predictive influence of postural BP on the development of hypertension are unknown, these findings may have important influences on identifying subjects at risk and also providing insight into disease pathogenesis.