Background/Aim: Radiofrequency ablation (RFA) is an increasingly utilised technique in patients with surgically-untreatable lesions. The effect of this therapy on circulating tumor cells (CTCs) is unknown. As far as we are aware of, this is the first study to evaluate the effects of RFA on CTCs in patients with malignant lung tumors immediately post-treatment. Patients and Methods: Nine patients with primary or metastatic lung tumors underwent RFA therapy from June to November 2013. Blood samples were taken before and after RFA, and filtered through the ScreenCell CTC capture device. Results: A general increase in CTCs in 7 out of the 9 cases was found, the largest increases were seen in the metastatic group. Conclusion: This study demonstrates that the manipulation and ablative procedure of lung tumors leads to immediate dissemination of tumor cells, the effects of which are unknown and require further investigation.