The contribution of hypertension to risk of all strokes and of nonembolic brain infarction in elderly black and white men and women is examined.The results of the Chicago Stroke Study show that hypertension is significantly associated with increased risk of nonembolic brain infarction, as well as all stroke, in this population of elderly black and white men and women. It is possible that 25% or more of the total incidence of stroke in persons 65 to 74 years of age may be attributable to hypertension.