Experimental evidence suggests that intercellular adhesion molecule-1 mediated leukocyte extravasation contributes to the pathogenesis of cerebral vasospasm. Simvastatin, an HMG-CoA reductase inhibitor, decreases intercellular adhesion molecule-1 expression and competitively inhibits leukocyte intercellular adhesion molecule-1 binding. We hypothesized that administration of simvastatin after the onset of subarachnoid hemorrhage (SAH) would attenuate perivascular granulocyte migration and ameliorate cerebral vasospasm in a rabbit model of SAH. New Zealand white rabbits (n = 15) underwent injection of autologous blood into the cisterna magna or sham surgery followed by subcutaneous injection of simvastatin (40 mg/kg) or vehicle 30 minutes, 24 hours, and 48 hours after SAH or sham surgery. Seventy-two hours later, basilar artery lumen diameter was measured by in situ perfusion/fixation and image analysis. CD-18 monoclonal antibody stained perivascular granulocytes and macrophages were counted under light microscopy. In vehicle treated rabbits, mean +/- standard deviation basilar artery diameter was reduced 3 days after SAH (n = 5) versus sham (n = 5) rabbits (0.49 +/- 0.08 mm versus 0.75 +/- 0.03 mm, P < 0.01). After SAH, mean +/- standard deviation basilar artery diameter was greater in simvastatin (n = 5) treated rabbits versus vehicle (n = 5) (0.63 +/- 0.04 mm versus 0.49 +/- 0.08 mm, P < 0.01). In vehicle treated rabbits, SAH resulted in an increase in the mean +/- standard deviation perivascular CD18 cell count (sham-vehicle, 2.8 +/- 2; SAH-vehicle 90 +/- 27; P < 0.01). Subcutaneous administration of simvastatin attenuated this increase in perivascular CD18-positive cells after SAH (SAH statin, 41.6 +/- 13; SAH vehicle, 90 +/- 27; P < 0.001). Subcutaneous administration of simvastatin after the onset of SAH attenuates perivascular granulocyte migration and ameliorates basilar artery vasospasm after experimental SAH in rabbits. 5-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors, such as simvastatin, may potentially serve as agents in the prevention of cerebral vasospasm after SAH.