Summary:Significant advances in our understanding of vasospasm include the definition of the time course of vasospasm, the ability to predict the location and severity of vasospasm based on a computed tomography scan obtained within five days of subarachnoid hemorrhage and the recognition of vasospasm as a significant adverse prognostic factor for outcome following aneurysmal subarachnoid hemorrhage. It is also recognized that the most important factor in the etiology of vasospasm is subarachnoid clot that causes vasospasm by hemolysis and release of spasmogenic compounds from the erythrocytes. The recent advances that have substantially reduced the morbidity and mortality from vasospasm include calcium channel antagonists such as nimodipine, hemodynamic therapy to improve cerebral blood flow, and transluminal angioplasty. Numerous therapies continue to be evaluated including subarachnoid clot lysis with tissue plasminogen activator, superselective intraarterial infusions of papaverine, and drugs such as tirilazad.