The distribution of blood pressure levels in elderly patients is described and the evidence that higher levels are associated with morbidity at this age is reviewed. In the absence of definitive evidence about the results of treating hypertension in the elderly, the physiological factors that have to be taken into account are surveyed with particular reference to aggravating cerebral ischaemia.More potent hypotensive agents should be avoided in older patients and in practice the decision on whether to treat may depend more on the clinical context than on the level of the blood pressure itself.