The present study was undertaken to assess the clinical use of power Doppler (PD) as a new tool for transcranial vessel imaging. Power Doppler displays the integrated power of the Doppler signal instead of the Doppler frequency shift used in the conventional color flow Doppler (CFD) technique. Twenty-one patients were evaluated who had intracranial malformations or arterial stenoses [4 middle cerebral artery (MCA) stenoses, 2 intracranial carotid stenoses, 7 arteriovenous malformations (AVM), 5 intracranial carotid aneurysms, 3 Moya-Moya syndromes]. The PD results were compared with those obtained from CFD and digital subtraction angiography (DSA). Power Doppler was able to visualize 3 of 4 MCA stenoses with greater morphological detail than CFD, whereas PD and CFD were equally effective in diagnosing carotid stenoses. All AVMs were visualized using PD as well as CFD, but again PD revealed more morphological details, in a manner similar to DSA. Power Doppler was also superior to CFD in imaging intracerebral aneurysms and pathological collateralization associated with Moya-Moya syndromes. It is evident from these data that PD permits reliable and detailed transcranial imaging and therefore is a superior method for visualizing intracerebral vascular malformations and arterial stenoses.