To determine whether contrast-enhanced ultrasound (CEUS) can aid in assessing treatment efficacy within the first 2 weeks after transarterial chemoembolization for hepatocellular carcinoma. Contrast-enhanced ultrasound was performed to detect residual tumor blood flow after 42 transarterial chemoembolization procedures in 33 patients who had hepatocellular carcinomas, and the results were compared with final tumor outcome. Twenty-nine CEUS studies were performed within 2 weeks after treatment and the remainder within 1 month. Phase-inversion low-mechanical-index real-time and intermittent imaging were performed after the intravenous injection of 0.5-2 mL US contrast medium by experienced radiologists blind to all other imaging findings. Nine tumors did not reach final outcome--patients were lost to follow-up or died without autopsy (n = 6) or tumors were retreated before final outcome was established (n = 3). Of the remaining 33 tumors, outcome was established by histology (n = 9), angiography (n = 14), tumor growth (n = 2), or by computed tomography and/or magnetic resonance imaging performed more than 6 months after treatment (n = 8). Twenty-three tumors were studied by CEUS within 2 weeks and 10 within 1 month after treatment. Of these 33 tumors, there were no false-negative results and one false-positive result. The only error occurred when the CEUS study was performed within 1 day after treatment. Residual tumor blood flow on CEUS performed at 2 or more days after transarterial chemoembolization may be predictive of tumor outcome that currently requires 3 months to be reliably detected by computed tomography and/or magnetic resonance imaging.