The aim of the current study was to evaluate the safety and the efficacy of radiofrequency thermal ablation (RFTA) for the treatment of nonsmall cell lung cancer (NSCLC) and isolated pulmonary metastases (METs) from colorectal cancer (CRC). A total of 31 patients (15 with NSCLCs and 16 with CRC lung METs), with 36 lung tumour nodules (mean+/-sd diameter: 22+/-8 mm, range: 10-35 mm) underwent computed tomography (CT)-guided RFTA using expandable electrodes. Contrast-enhanced CT was performed before and after (immediately and 30+/-5 days) each RFTA session to assess immediate results and complications and repeated 3 and 6 months post-RFTA, as well as every 6 months thereafter, to evaluate long-term results. Complete radiological necrosis was defined as a nonenhancing area at the tumour site that was equal to or larger than the treated tumour; persistence of enhancement at the tumour site indicated incomplete treatment. Local recurrence was defined as an increase in tumour size and/or enhancing tissue at the tumour site. Complete radiological necrosis of the 36 tumours was achieved with 39 RFTA sessions and 42 electrode insertions. No major complications or deaths were observed. Six patients experienced mild-to-moderate pain during the procedure. There were five cases of pneumothorax, none requiring drainage and four cases of pneumonia, which were successfully treated with antibiotics. After a mean follow-up of 11.4+/-7.7 months (range of 3-36 months), the overall local recurrence rate was 13.9% (20 and 9.5% for NSCLC and CRC-METs patients, respectively). Nineteen of the 31 (61.3%) patients were alive (15 apparently disease free) and 12 (38.7%) had died (three from causes unrelated to their cancer). Radiofrequency thermal ablation seems to be a safe, effective method for producing complete ablation of small nonsmall cell lung cancers and pulmonary colorectal cancer metastases.