Widespread reluctance to treat hypertension during acute stroke is based on historical accounts of unfavorable outcomes of treatment that were badly done: therapies that cannot be controlled, such as sublingual nifedipine, oral or intramuscular antihypertensive drugs may drop blood pressure precipitously, leading to worsening of ischemia. Case fatality in stroke obeys a U-shaped relationship: blood pressures that are either too low or too high are associated with worse outcomes both in ischemic stroke and in intracerebral hemorrhage. Very high blood pressures should be lowered in acute stroke, and there are some circumstances in which high blood pressure must be treated despite the presence of stroke. To avoid worsening of ischemia by reduction in cerebral blood flow, it is necessary to treat high blood pressure in acute stroke with drugs that can be controlled; this usually means giving drugs by intravenous infusion; however, there is recent evidence that transdermal administration of nitrates, which can be removed if pressure is too low, is a convenient alternative that does not reduce cerebral blood flow in acute stroke.