Although its status as a neuroprotectant is controversial, etomidate is often employed for pharmacologic cerebral protection in aneurysm surgery. One purported advantage of etomidate over thiopental is its hemodynamic stability. This study examined the cardiovascular effects of etomidate given for electroencephalographic (EEG) burst suppression during cerebral aneurysm clipping in humans and the direct effects of etomidate on arteries in vitro. The charts of intracranial aneurysm surgery patients were retrospectively reviewed to determine the dose of etomidate employed, the frequency of concurrent vaspressor administration, and whether hemodynamic changes were associated with etomidate use. Against a background of balanced anesthesia, the dose of etomidate to induce burst suppression was 0.73 ± 0.49 mg/kg (mean ± SD) and the main-tenance dose was 48 ± 30 μg/kg/min. Etomidate produced an immediate decrease in mean arterial pressure that was sustained in patients who did not receive vasopressor support. During etomidate administration, 48% of patients (10 of 21) received some form of vasopressor support such as phenylephrine or ephedrine, and 62% of patients (13 of 21) receiving isoflurane had the anesthetic discontinued or its inspired concentration decreased. Etomidate in vitro produced dose-dependent relaxation of human internal mammary arterial rings that had been preconstricted by potassium or norepinephrine. Etomidate, in EEG burst suppression doses, decreases mean arterial pressure in anesthetized patients undergoing cerebral aneurysm surgery. One mechanism of etomidateinduced hypotension may be direct relaxation of vascular smooth muscle, because etomidate directly dilates preconstricted human arteries in vitro.