OBJECTIVE The goal was to evaluate the efficacy and reliability of intraoperative microvascular doppler sonography for the assessment of cerebral hemodynamics in aneurysm surgery. METHODS For 35 patients who underwent surgery for the treatment of 42 intracranial aneurysms, microvascular doppler sonography with a 20-MHz probe (1-mm diameter) was used before and after clip application, to confirm the obliteration of aneurysms. Assessment of the patency of the parent vessels and all branching arteries was performed. The findings from doppler sonography were confirmed with either intraoperative angiography or immediate postoperative angiography. RESULTS The 1-mm microprobe was able to insonate all vessels of the circle of Willis and their major branches; furthermore, perforating arteries were reliably insonated. For 11 patients (31%), doppler sonography exposed parent artery or branching artery stenosis or occlusion and guided the immediate adjustment of aneurysm clip placement. The findings from intraoperative microvascular doppler sonography correlated with findings from angiography in all cases. There were no complications of microvascular doppler probe use. CONCLUSIONS Intraoperative microvascular doppler sonography is a safe, instantaneous, effective, reliable, and cost-effective method for documenting the patency of parent vessels, arterial branches, and major perforators and the complete occlusion of cerebral aneurysms. This technique can be reliably used, in many instances, instead of intraoperative angiography for the surgical treatment of aneurysms.