We evaluated the efficacy and safety of radiofrequency (RF) ablation for hepatocellular carcinoma (HCC) in presumably high-risk locations. Between February 1999 and December 2001, we performed RF ablation on 1,419 nodules in 636 consecutive HCC patients, of which 231 nodules in 207 patients were in high-risk locations, defined as less than 5 mm from a large vessel or an extrahepatic organ. Eighty-one patients had a nodule adjacent to a large vessel, 145 patients had a nodule adjacent to an extrahepatic organ, of whom 19 also had one adjacent to a large vessel. Early complications and local tumor progression were analyzed with regard to the location of each nodule. The mean nodule diameter and average number per patient were 27 mm and 2.3, respectively. Early complications, within 30 days after ablation, occurred in 12 of 207 patients (5.8 %) with a nodule in a high-risk location and in 15 of 429 patients (3.5 %) without ( P = .1776). There was no significant difference in local tumor progression rate between nodules in high-risk locations (1 year: 2.1%, 2 years: 3.1%, 3 years: 3.1%) and those elsewhere (1 year: 0.6%, 2 years: 1.7%, 3 years: 2.5%) ( P = .2745). In conclusion , HCC nodules adjacent to a large vessel or extrahepatic organ were treated with RF ablation without compromising the efficacy of the procedure. However, even though without significant difference, some complications occurred at risky locations and need to be carefully considered. (Hepatology 2006;43:1101–1108.)