Power Doppler is a new ultrasound technique based on the visualization of the Doppler power spectrum. In 22 patients with different lesions of brain-supplying vessels the results of power Doppler ultrasound were compared with those of digital subtraction angiography and conventional color Doppler ultrasound. In patients with intracranial high-degree stenoses, power Doppler was largely free of those artifacts that occur with conventional color Doppler (e.g., echoshadowing and aliasing). The vessel lumen was seen in all patients with more than 80% stenoses. Power Doppler was superior to conventional color Doppler in visualizing both middle cerebral artery stenosis and intracerebral aneurysms. Power Doppler visualization of intracranial pathology was similar to visualization by digital subtraction angiography. Power Doppler appears to be a valuable tool in the noninvasive imaging of intracranial and extracranial pathological vascular conditions.