High-intensity focused ultrasound (HIFU) is a noninvasive method that can cause complete coagulation necrosis without requiring the insertion of any instruments. The purpose of this study was to evaluate the safety and usefulness of HIFU assisted by ultrasound-computed tomography three-dimensional (US-CT3D) dual imaging for the treatment of hepatocellular carcinoma (HCC). The HIFU system (Chongqing Haifu Tech, Chongqing, China) was used under ultrasound guidance. HIFU ablation was performed in 10 patients with small HCC (≤3 lesions, ≤3 cm in diameter). By transferring the sagittal or axial plane of the 3D US and the CT volume data into a ZioM900 workstation, multiplanar reconstruction images were displayed in a manner resembling conventional US to assist the HIFU treatment. The patients in whom good visualization using B-mode sonography could not be achieved because of the influence of multi-reflections, rib shadows, and unclear tumor margins were successfully treated under the guidance of US-CT 3D dual imaging. The 3D US images obtained as part of the US-CT 3D dual imaging had a high resolution and were useful for examining the area of HCC invasion and for determining the extent of the ablation area. The CT images, which are not influenced by bone shadows or multi-reflections, were useful for detecting the tumors and for visualizing the presence of the intestines in the sonication zone. HIFU treatments were successfully performed in all of the patients with the assistance of US-CT 3D dual imaging.