The contribution of hypertension to the development of cardiovascular disease in older subjects of the Framingham Study was systematically examined. Because of its high prevalence and sustained impact as age increases, hypertension emerged as the dominant risk factor for cardiovascular disease in older persons. The prevalence of definite hypertension increased with age to include about 40% of older men and 50% of older women in the Framingham cohort. The total incidence of cardiovascular disease rose progressively with increasing systolic blood pressure, irrespective of age and sex. Risk in the elderly of both sexes was approximately twice as great as that observed for younger persons at the same levels of systolic blood pressure. The risk of cardiovascular disease rose proportionally with increasing diastolic blood pressure in older men; however, this trend was blunted in older women. These findings suggest a more consistent role for systolic blood pressure as a predictor of cardiovascular disease in older persons. When individuals were classified according to hypertensive status, the overall risk for cardiovascular events and deaths due to cardiovascular disease was two to three times higher in subjects with definite hypertension compared with normotensives for all age and sex groups considered. Again, the risk was two to three times higher in older persons and nearly always higher in men than in women. Thus, whether predominantly systolic or diastolic, hypertension is clearly dangerous in terms of both absolute and relative risk as well as risk gradients for a broad spectrum of cardiovascular disease events in the elderly.