We evaluated the usefulness of contrast-enhanced harmonic grayscale sonography (contrast US) to assess the therapeutic efficacy of transcatheter arterial embolization (TAE) with iodized oil, percutaneous ethanol injection (PEI), radiofrequency ablation (RFA), and combination therapy for patients with hepatocellular carcinoma (HCC), and we evaluated the patients for incomplete local treatment during the follow-up periods. Lesions were considered to contain viable tumor residue when hypervascular enhancement was observed within the tumor. We concluded that adequate tumor necrosis had occurred in the lesions when an oval or round perfusion defect with distinct margins was observed in the late vascular phase of contrast ultrasound after transcatheter arterial embolization. Further, we concluded that adequate tumor necrosis had occurred when lesions treated by percutaneous ethanol injection or radiofrequency ablation showed a nonenhancing area in the late vascular phase of contrast ultrasound whose area exceeded that of the hypervascular enhancement seen in the early or late vascular phase of contrast ultrasound before treatment. Because artifacts were produced by accumulation of iodized oil in the tumor, hardly any of the hepatocellular carcinoma lesions could be evaluated for the presence of tumor residue by helical CT. However, contrast ultrasound enabled us to distinguish between viable and necrotic portions of hepatocellular carcinoma lesions, because iodized oil deposition did not interfere with the perfusion images. Local recurrence within about 6 months after therapy was observed by helical CT in all lesions in which contrast ultrasound had detected viable tumor residue. Lesions in which adequate tumor necrosis was observed by contrast ultrasound after transcatheter arterial embolization, percutaneous ethanol injection, radiofrequency ablation, or combined therapy exhibited a low rate of local recurrence during the follow-up period (mean, 24 months). Contrast ultrasound proved useful for evaluating the therapeutic effect of transcatheter arterial embolization percutaneous ethanol injection, radiofrequency ablation, or combined therapy of hepatocellular carcinoma, and it was also useful for guiding percutaneous ethanol injection, radiofrequency ablation, and other additional treatments.