OBJECTIVE: We describe the rates and potential risk factors of complications of radiofrequency ablation of hepatic tumors. SUBJECTS AND METHODS. Over a 5-year period, 312 patients underwent 350 sessions of radiofrequency ablation (124 intraoperative and 226 percutaneous) for treatment of 582 liver tumors including 115 hepatocellular carcinomas and 467 metastatic tumors. The chi-square test was used for a group-to-group comparison of the occurrence of adverse events. RESULTS: Thirty-seven (10.6%) adverse events and five (1.4%) deaths were related to radiofrequency treatment. The deaths were caused by liver insufficiency (n = 1), colon perforation (n = 1), and portal vein thrombosis (n = 3). Portal vein thrombosis was significantly (p < 0.00001) more frequent in cirrhotic livers (2/5) than in noncirrhotic livers (0/54) after intraoperative radiofrequency ablation performed during a Pringle maneuver. Liver abscess (n = 7) was the most common complication. Abscess occurred significantly (p < 0.00001) more frequently in patients bearing a bilioenteric anastomosis (3/3) than in other patients (4/223). We encountered five pleural effusions, five skin burns, four hypoxemias, three pneumothoraces, two small subcapsular hematomas, one acute renal insufficiency, one hemoperitoneum, and one needle-tract seeding. The 6.3% of minor complications did not require specific treatment or a prolonged hospital stay. Among the 5.7% major complications, 3.7% required less than 5 days of hospitalization for treatment or surveillance and 2% required more than 5 days for treatment. CONCLUSION: Radiofrequency ablation of liver tumors is a well-tolerated technique, but caution should be exercised when treating patients with a bilioenteric anastomosis, and radiofrequency ablation during vascular occlusion in cirrhotic livers should be avoided.