Experimental evidence has indicated the benefits of simvastatin for the treatment of subarachnoid hemorrhage. Two randomized placebo-controlled pilot trials that used the highest clinically approved dose of simvastatin (80 mg daily) gave positive results despite the fact that a lower dose of simvastatin (40 mg daily) did not improve clinical outcomes. We hypothesized that a high dose of 80 mg of simvastatin daily for 3 weeks would reduce the incidence of delayed ischemic deficits after subarachnoid hemorrhage compared with a lower dose (40 mg of simvastatin daily) and lead to improved clinical outcomes. The study design was a randomized controlled double-blinded clinical trial. Patients with aneurysmal subarachnoid hemorrhage (presenting within 96 hours of the ictus) from 6 neurosurgical centers were recruited for 3 years. The primary outcome measure was the presence of delayed ischemic deficits, and secondary outcome measures included a modified Rankin disability score at 3 months and an analysis of cost-effectiveness. No difference was observed between the groups treated with the higher dose or the lower dose of simvastatin in the incidence of delayed ischemic deficits (27% versus 24%; odds ratio, 1.2; 95% confidence interval, 0.7-2.0; P=0.586) or in the rate of favorable outcomes (modified Rankin Scale score, 0-2) at 3 months (73% versus 72%; odds ratio, 1.1; 95% confidence interval, 0.6-1.9; P=0.770). High-dose simvastatin treatment should not be prescribed routinely for aneurysmal subarachnoid hemorrhage. http://www.clinicaltrials.gov. Unique identifier: NCT01077206.