Several cerebral pathologic processes thought to result from derangements in vascular autoregulatory mechanisms show reversible abnormalities on computed tomographic and magnetic resonance images. The hypertensive encephalopathies are characterized by intracranial abnormalities due to subacutely elevated blood pressure; these entities include hypertensive encephalopathy, preeclampsia and eclampsia, and cyclosporine toxicity. Imaging studies reveal symmetric confluent lesions with mild mass effect and patchy enhancement centered in the immediate subcortical white matter of the occipital lobes. The uremic encephalopathies are characterized by intracranial abnormalities due to an elevated level of blood urea nitrogen; these entities include uremia and glomerulonephritis, hemolytic-uremic syndrome, and thrombotic thrombocytopenic purpura. Imaging studies reveal multiple areas of symmetric edema in the basal ganglia; in severe cases, focal infarcts with or without hemorrhage can be seen. As radiologists become more familiar with these entities, cases can be recognized earlier in the disease process, allowing more timely initiation of appropriate therapy.