Malignant hypertension still constitutes a medical emergency, particularly when complicated by renal failure, encephalopathy, or left ventricular failure. A shift to the right of the autoregulatory curve of cerebral blood flow (and probably of renal blood flow) is known to occur in patients with hypertension. Local cerebral edema, complicating the malignant phase, is likely to aggravate this trend. While inadequate or tardy treatment leads to encephalopathy, renal and cardiac failure, over aggressive treatment may also result in damage to brain, heart, and kidney. Recent reports of neurological damage, sometimes fatal, following aggressive hypotensive treatment suggests the need for a reappraisal of current practices. More investigation is needed to determine the effects of the various classes of antihypertensive drugs on organ perfusion, particularly of brain, heart, and kidney, in both normal and hypertensive humans. Other hypertensive crises include raised arterial pressure in association with acute dissection of the aorta and in the presence of stroke or subarachnoid hemorrhage. While there is agreement about the need for urgent hypotensive treatment in patients with aortic dissection, there is no information with which to base rational decisions in the management of high arterial pressure in the acute phase of stroke or subarachnoid hemorrhage.