Radiofrequency ablation (RFA) of liver tumors was first proposed in 1990. New technologies enable us to produce liver thermal lesions of approximately 3-3.5 cm in diameter; RFA has consequently become an emerging percutaneous therapeutic option both for small hepatocellular carcinoma (HCC) and for non-resectable liver metastases, mainly from colorectal cancer. New devices (for example, triplet of cooled needles, wet needles) and combined therapies (tumor ischemia and RFA) have made it possible to treat large tumors. RFA can be carried out by a percutaneous, laparoscopic or laparotomic approach. Percutaneous RFA can be performed with local anaesthesia and mild sedation; deep sedation or general anaesthesia are also used. The guidance system is generally represented by ultrasound. CT or MR examinations are the more sensitive tests for assessing therapeutic results. The series of patients treated with RFA allow the technique to be considered as effective and safe, achieving a relatively high rate of cure in properly selected cases; it should be classified as curative/effective treatment for HCC, replacing percutaneous ethanol injection. The complication rate of RFA is low but not negligible; key elements in a strategy to minimize them are identified.