Power Doppler sonography (PD) is a technique that displays the strength of the Doppler signal, rather than the flow velocity and directional information. Its increased flow sensitivity and better vascular delineation have been used to document the presence and characteristics of flow in vessels that are poorly imaged with conventional color Doppler (CD), to identify areas of ischemia, to demonstrate inflammatory hyperemia or increased and irregular flow in tumors, as well as to assess serial vascular changes related to interval therapy. The present review reports the general principles of PD, portrays the results of clinical studies available in the literature, and suggests future trends of development.