This retrospective study was conducted to review the complications of lung radiofrequency (RF) ablation and to clarify the effects of inflammation after lung RF ablation on mortality and morbidity. Complications were evaluated by reviewing medical records on an RF session basis. The C-reactive protein (CRP) value was used as an indicator of inflammation and was measured before and every 1-2 days during the hospital stay after RF ablation. The relationships between CRP values and patient baselines were evaluated to identify factors affecting lung inflammation. 130 patients who underwent 327 lung RF ablation sessions were enrolled in this study. The major complication rate was 18.3% (60/327). Inflammation-related complications such as interstitial pneumonia (n = 2) and aseptic pleuritis (n = 2) developed in four sessions (1.2%). Death occurred in two patients with interstitial pneumonia (0.6%). The mean CRP value increased significantly from 1.3+/-2.6 mg dl(-1) to 3.4+/-5.6 mg dl(-1) (p<0.01) after RF ablation. Large tumour size (>or=2 cm) and previous external-beam radiotherapy were significant factors associated with an increased CRP value in both univariate and multivariate analyses. In conclusion, although the incidence rate is low, fatal lung inflammation may develop after lung RF ablation. Large tumour size and previous external-beam radiotherapy are risk factors for severe lung inflammation.