Background: Percutaneous image-guided radiofrequency ablation is being promoted as a novel technique with a low morbidity rate in the treatment of inoperable lung tumors. The purpose of this study was to assess the incidence and risk factors of various complications after radiofrequency ablation of pulmonary neoplasms. Methods: The clinical and treatment-related data regarding 129 consecutive percutaneous radiofrequency ablation treatment sessions for 100 patients with inoperable lung tumors were collected prospectively. Univariate and multivariate analyses were conducted to identify significant risk factors associated with postprocedural overall morbidity, pleuritic chest pain, hemoptysis, pneumothorax, pleural effusions, and chest drain requirement. Results: There was no postprocedural mortality. The overall morbidity rate was 43% (n = 55 of 129). The most common adverse effect was pneumothorax, occurring in 32% (n = 41 of 129) of treatment sessions. Other significant complications included pleuritic chest pain (18%, n = 23 of 129), hemoptysis (7%, n = 9 of 129), pleural effusions (12%, n = 15 of 129), and chest drain insertion (20%, n = 26 of 129). Both univariate and multivariate analyses identified more than two lesions ablated per session as a significant risk factor for overall morbidity, pneumothorax, and chest drain insertion, but not for pleuritic pain, hemoptysis, and pleural effusions. Length of the ablation probe trajectory greater than 3 cm was an additional independent risk factor for overall morbidity and pneumothorax. Hilar location of lung tumor/s was the only independent risk factor associated with the increased incidence of hemoptysis. Conclusions: Radiofrequency ablation for lung tumors can be considered as a safe and technically feasible procedure with acceptable incidence of complications.