Cerebral vasospasm following subarachnoid hemorrhage (SAH) is the most common cause of morbidity and mortality. Recent studies indicate that Rho-kinase play an important role in the occurrence of such cerebral vasospasm. Eicosapentaenoic acid (EPA) inhibits sphingosylphosphorylcholine (SPC)-induced Rho-kinase activation in vitro. So this study examines whether EPA prevents cerebral vasospasm occurrence after SAH in patients.