Cerebral vasospasm is the classic cause of delayed neurological deterioration leading to cerebral ischemia and infarction, and thus, poor outcome and occasionally death, after aneurysmal subarachnoid hemorrhage (SAH). Advances in diagnosis and treatment, principally nimodipine, intensive care management, hemodynamic manipulations, and endovascular neuroradiology procedures, have improved the prospects for these patients, but outcomes remain disappointing.