Hypertension causes marked adaptive changes in the cerebral circulation. The excess risk of stroke associated with hypertension is eliminated in controlled trials of antihypertensive treatment. Such treatment may even prevent transient ischaemic attacks in the elderly. In rare cases, overzealous antihypertensive treatment may cause cerebral ischaemia, especially in the initial treatment of very severe hypertension. Headache may occasionally be caused by severe hypertension, which may also lead to the rare syndrome of acute hypertensive encephalopathy. Finally, the importance of white-matter lesions, or leukoaraiosis, in hypertension is not yet fully established.