OBJECTIVE To evaluate applicability of power Doppler sonography (PDS) in differential diagnosis of small hepatocellular carcinoma (SHCC) and adenomatous hyperplastic nodule (AHN). METHODS Twenty-two cases of SHCC and 15 cases of AHN were investigated by PDS and the findings were compared with those of digital subtraction angiography (DSA). RESULTS The rates of arterial and portal flow in an afferent tumor vessel were 86.4% and 40.9% in SHCCs, respectively. The rate of portal flow in an afferent tumor vessel was 60.0% in AHNs, while no arterial flow was detected (P < 0.01). In addition, PDS revealed a constant flow in an efferent tumor vessel (50.0%) continuing to a portal branch in 10 (45.5%) of the 22 SHCCs cases to a hepatic vein in 1 (4.5%) of the 22 SHCCs, but to nothing else in the AHNs (P < 0.01). CONCLUSIONS Power Doppler sonography is of value in distinguishing SHCC from AHN, and arterial afferent tumor vessels from constant flow efferent tumor vessels at PDS.