The therapeutic efficacy of intravenous nimodipine to treat the syndrome of delayed ischemic deterioration or vasospasm after subarachnoid hemorrhage caused by a ruptured aneurysm was investigated in a randomized, double-blind, placebo-controlled multicenter study. A total of 188 patients (nimodipine (N) = 102, placebo (P) = 86) were enrolled in the study, both pre- and postoperatively, within 24 hours of clinical deterioration connected with vasospasm or within 24 hours of arteriography that identified vasospasm. After 61 patients were excluded for not meeting study criteria or for protocol violation, the results were supported by 127 validated case reports: 73 patients received intravenous treatment with nimodipine, and 54 were given placebo. Analysis of the main criterion of efficacy, the number of deaths and of patients with severe deficit related to vasospasm alone, showed a significant statistical difference (N = 8 (19%), P = 17 (49%), P = 0.01). The risk of death or disability was reduced by 66% in the treated group. Analysis of this criterion by type of inclusion (clinical or angiographic) also showed a significant reduction in the clinical group (P = 0,05), but there was no difference in the angiographic group. The risk of mortality connected with vasospasm was reduced by 82%, but analysis by group showed that there was no significant difference for those patients included on clinical criteria, whereas mortality was reduced to a much greater extent in the angiographic group. These results demonstrate the therapeutic efficacy of nimodipine in reducing secondary ischemic brain damage in patients already suffering from angiographic vasospasm or delayed ischemic deterioration.