The aim of this study was to evaluate the efficacy of and tolerance for radiofrequency thermoablation (RFTA) in patients with hepatocellular carcinoma (HCC). From March 1999 to September 2001, a total of 56 patients (46 men and 10 women) whose mean age was 67.8 years (range 51 to 76 years) underwent RFTA for 71 HCCs at our institution. RFTA was carried out in 45 patients with one lesion less than 6 cm in diameter, in seven patients with two lesions less than 4 cm in diameter each, and in four patients with three lesions less than 3 cm in diameter each. The mean diameter of the lesions was 4.1 cm (range 0.8 to 6.0 cm). The etiology of the cirrhosis was alcoholism in 31 patients, post-hepatitis C in 19 patients, post-hepatitis B in four patients, and hemochromatosis in two patients. Forty-five patients were classified as Child stage A and 11 were Child stage B. No ascites, prothrombin time >60%, and platelet count <60,000/mm(3) were needed. Two types of cooled needles were used depending on the size of the lesion (a needle 15 cm in length was used for 2 or 3 cm tumors, and a cluster of needles was used for tumors larger than 4 cm). Helical computed tomography was performed 8 weeks after treatment. The main criterion for a complete response was the presence of a hypodense lesion without contrast enhancement. Mean follow-up was 14 months. Complete tumor destruction was achieved in 50 (89.2%) of 56 patients after one session and in 52 (92.8%) of 56 after two sessions. Twelve months later, a complete response was confirmed in 45 patients (80.3%), four patients had a local recurrence and new liver nodules, and three patients had died (one of bone metastasis, one of acute alcoholic hepatitis, and one of bronchial carcinoma). Thirty-nine patients (69.6%) were still in complete remission 36 months later, and a new HCC had developed in six patients. At 36 months 49 of 56 patients were alive and 39 of 56 were free of disease. Patients with HCCs that developed following viral cirrhosis had a worse prognosis than those with HCCs that occurred after alcoholic cirrhosis (2-year survival, 57.7% vs. 77.7%; P=0.0241). It was concluded that radiofrequency ablation is an effective treatment for HCC, although the prognosis is better in patients who develop HCC after alcoholic cirrhosis compared to those in whom HCC occurs after viral cirrhosis.