OBJECTIVE: The objective of our study was to evaluate the efficacy and safety of radiofrequency ablation of hepatic metastases performed either percutaneously for treatment of hepatic metastases in patients deemed ineligible for surgery or intraoperatively during partial hepatectomy to destroy unresectable metastases. SUBJECTS AND METHODS: Sixty-eight patients with 121 hepatic metastases (<5 metastases per patient) that were mainly colorectal in origin underwent 76 sessions of radiofrequency ablation with cooled-needle electrodes under sonographic guidance. Twenty-one patients with 33 metastases of 5-20 mm in diameter (mean +/- SD,13 +/- 7 mm) underwent intraoperative radiofrequency ablation. Forty-seven patients with 88 metastases of 10 to 42 mm in diameter (mean +/- SD, 26 +/- 9 mm) were treated with percutaneous radiofrequency ablation. Procedure efficacy was evaluated with dynamic enhanced CT and MR imaging performed 2, 4, and 6 months after treatment and then every 3 months. RESULTS: Radiofrequency ablation allowed eradication of 91% of the 100 treated metastases that were followed up for 4-23 months (mean, 13.7 months). Tumor control was equivalent for percutaneous radiofrequency ablation (90%) and for intraoperative radiofrequency ablation (94%). Failure to achieve tumor control occurred mostly with the largest tumor nodules. One bilioperitoneum and two abscesses were the major complications encountered after treatment of 121 metastases with a follow-up of more than 2 months. CONCLUSION: Radiofrequency ablation appears to be a promising therapeutic modality capable of extending the possibilities of partial hepatectomy and of efficiently treating small metastases percutaneously.