We compared the detection of blood flow in hepatocellular carcinomas with a diameter ≤3 cm between power Doppler ultrasound imaging (PDI), dynamic computed tomography (CT), dynamic magnetic resonance imaging (MRI), and hepatic angiography. We also investigated the usefulness of PDI for evaluating the efficacy of local therapy for hepatocellular carcinoma (HCC) by comparing pretreatment and posttreatment PDI, dynamic CT, and dynamic MRI findings. The tumor detection rate with PDI, dynamic CT, dynamic MRI, and hepatic angiography was 57%, 76%, 76%, and 80%, respectively. In 13 patients with 15 nodules which showed PDI blood flow signals before treatment, the posttreatment blood flow detection rate with PDI, dynamic CT, and dynamic MRI was 47%, 25%, and 25%, respectively. Viable residual tumor cells were found on biopsy of two out of five nodules that showed blood flow signals on PDI, but showed no early staining on dynamic CT and/or dynamic MRI. PDI is a simple, non-invasive procedure that can be done repeatedly at the bedside in real-time. In the future, PDI may become an important imaging modality in the management of HCC.