PURPOSE: To evaluate the efficacy and safety of radiofrequency (RF) ablation for the treatment of small hepato-cellular carcinoma (HCC). MATERIALS AND METHODS: Forty-four patients with 51 HCCs underwent ultrasound guided RF ablation using ex-pandable needle electrodes and a monopolar RF generator. The patients were not considered suitable candidates for surgery or declined this option, and had no history of previous treatment. Mean tumor diameter was 2.5 cm (range, 1.0 -4.0 cm). Therapeutic efficacy was evaluated by means of three-phase helical computed tomography (CT) performed at least one month after the completion of ablation. The recurrence rate was also evaluated by follow-up CT at least four months after treatment. RESULTS: Using RF ablation, complete necrosis was achieved in 48 of 51 tumors (94%). Among 20 patients in whom follow-up CT was performed at least four months after ablation, one (5%) showed marginal recurrence and in another (5%) there was recurrence in remote liver parenchyma. We experienced neither procedure-re-lated mortality nor major complications which required specific treatment. Three minor complications (one small pneumothorax and two cases of intraperitoneal bleeding) occurred, but these disappeared without specific treatment. CONCLUSION: RF ablation using an expandable needle electrode showed a high rate of complete necrosis and a low rate of complications. The technique is therefore considered effective and safe for the local control of small HCCs.