BACKGROUND: Positron emission tomography (PET) with 18F-fluoro-2-deoxy-D-glucose (18F-FDG) is useful in detecting distant metastases from a variety of malignancies. However, its efficiency in detecting distant metastases from hepatocellular carcinoma (HCC) has not been investigated. The aim of this study was to evaluate the usefulness of 18F-FDG PET for the detection of extrahepatic metastases from HCC. METHODS: Nineteen patients suspected of having extrahepatic HCC underwent 18F-FDG PET. Fourteen patients (group A) had extrahepatic lesions, which were detected by conventional studies. In five patients (group B), conventional imaging showed no extra- or intrahepatic lesions, but the tumor marker levels were elevated. The PET results were compared with those obtained by histopathology or by clinical follow-up. RESULTS: The detection rate of 18F-FDG PET was 83% (24 of 29 metastases) for extrahepatic metastases larger than 1 cm in greatest diameter and 13% (1 of 8 metastases) for lesions less than or equal to 1 cm. PET revealed two bone metastases not depicted by bone scan, and detected the nodal metastasis and intestinal metastases inconclusive on computed tomography. Extrahepatic lesions were resected in 5 patients of group A on the basis of PET findings. In all patients of group B, PET results were true negative for extrahepatic metastases, but HCCs were detected in the liver within 4 months in 4 patients. These were no false-positive lesions in either group. CONCLUSIONS: This preliminary study suggested that 18F-FDG PET could provide additional information and contribute to the management of HCC patients suspected of having extrahepatic metastases.