Cerebral vasospasm and delayed cerebral ischemia remain common complications of aneurysmal subarachnoid hemorrhage (SAH), and yet therapies for cerebral vasospasm are limited. Despite a large number of clinical trials, only calcium antagonists have strong evidence supporting their effectiveness. The purpose of this work was to perform a systematic review of the literature on the treatment of cerebral vasospasm. A literature search for randomized controlled trials of therapies used for prevention or treatment of cerebral vasospasm and/or delayed cerebral ischemia was conducted, and 41 articles meeting the review criteria were found. Study characteristics and primary results of these articles are reviewed. Key indicators of quality were poor when averaged across all studies, but have improved greatly over time. The only proven therapy for vasospasm is nimodipine. Tirilazad is not effective, and studies of hemodynamic maneuvers, magnesium, statin medications, endothelin antagonists, steroid drugs, anticoagulant/antiplatelet agents, and intrathecal fibrinolytic drugs have yielded inconclusive results. The following conclusions were made: nimodipine is indicated after SAH and tirilazad is not effective. More study of hemodynamic maneuvers, the effectiveness of other calcium channel antagonists such as nicardipine delivered by other routes (for example intrathecally), magnesium, statin drugs, endothelin antagonists, and intrathecal fibrinolytic therapy is warranted. There is less enthusiasm for the study of steroid drugs and anticoagulant/antiplatelet agents because they entail more risks and investigations so far have shown little evidence of efficacy. The study of rescue therapy such as balloon angioplasty and intraarterial vasodilating agents will be difficult. The quality of clinical trials should be improved.