The majority of patients with primary of metastatic hepatic tumors are not candidates for resection, because of tumor size, location near major intrahepatic blood vessels precluding a margin-negative resection, multifocality, or inadequate hepatic function related to coexistent cirrhosis. Radiofrequency ablation (RFA) is an evolving technology being used to treat patients with unresectable primary and metastatic hepatic cancers. RFA produces coagulative necrosis of the tumor through local tissue heating. Liver tumors are treated percutaneously, laparoscopically, or during laparotomy, using ultrasonography to identify tumors and to guide placement of the RFA needle electrode. For tumors smaller than 2.0 cm in diameter, one or two deployments of the monopolar multiple-array needle electrode are sufficient to produce complete coagulative necrosis of the tumor. However, with increasing size of the tumor, there is a concomitant increase in the number of deployments of the needle electrode and the overall time necessary to produce complete coagulative necrosis of the tumor. In general, RFA is a safe, well-tolerated, effective treatment for unresectable hepatic malignancies less than 6.0 cm in diameter. Effective treatment of larger tumors awaits the development of more powerful, larger array monopolar and bipolar RFA technologies.