BACKGROUND: Propofol may cause perioperative bleeding because it has an inhibitory effect on platelet aggregation and an accelerative effect on blood fibrinolysis in vitro. The aim of this study was to evaluate the perioperative effect of propofol anesthesia on blood coagulation and fibrinolysis with a thromboelastograph in patients undergoing clipping of cerebral aneurysms. METHODS: Fifteen patients who had cerebral aneurysms and no history of coagulation disorders were studied. Anesthesia was induced with a target controlled infusion of propofol to reach a calculated target blood concentration of 5ng/ml, and in addition, fentanyl 2ng/kg, lidocaine 1 mg/kg, esmolol 0.3 mg/kg and vecuronium 0.1 mg/kg were given intravenously. Anesthesia was maintained by propofol at target concentrations of 3 - 5ng/ml with nitrous oxide (67%) and oxygen (33%). The hemoglobin concentration, platelet count and a thromboelastogram were measured at before, during and after anesthesia. RESULTS: There was no significant difference in the perioperative hemoglobin concentration and platelet count. In terms of the thromboelastogram, r time (reaction time for clot formation) and k time (clot formation time) during and after anesthesia were shorter than those before anesthesia (P < 0.05), the alpha angle (rate of clot growth) during and after anesthesia was increased more than that before anesthesia (P < 0.05), and there was no significant difference in the perioperative fibrinolytic index. CONCLUSIONS: These results indicate that propofol anesthesia has no effect on anticoagulation and fibrinolysis in patients undergoing clipping of cerebral aneurysms in terms of the thromboelastogram, whereas, it showed a perioperative hypercoagulability. Therefore a clinical dosage of propofol may be used for neurosurgery without inhibition of coagulation.