Purpose To retrospectively evaluate the feasibility, safety, and efficacy of radiofrequency ablation (RFA) of lung tumors located near the diaphragm. Materials and methods A total of 26 patients (15 men, 11 women; mean age, 61.5 years ± 13.0 [SD]) with a total of 29 lung tumors near the diaphragm (i.e., distance < 10 mm) were included. Mean tumor diameter was 11.0 mm ± 5.3 (SD) (range, 2–23 mm). Efficacy of RFA, number of adverse events and number of adverse events with a grade ≥ 3, based on the National Cancer Institute Common Terminology Criteria for Adverse Events, version 4.0, were compared between patients with lung tumors near the diaphragm and a control group of patients with more distally located lung tumors (i.e., distance ≥ 10 mm). Results RFA was technically feasible for all tumors near the diaphragm. Four grade 3 adverse events (1 pneumothorax requiring pleurodesis and 3 phrenic nerve injuries) were observed. No grade ≥ 4 adverse events were reported. The median follow-up period for tumors near the diaphragm was 18.3 months. Local progression was observed 3.3 months after RFA in 1 tumor. The technique efficacy rates were 96.2% at 1 year and 96.2% at 2 years and were not different, from those observed in control subjects (186 tumors; P = 0.839). Shoulder pain (P < 0.001) and grade 1 pleural effusion (P < 0.001) were more frequently observed in patients with lung tumor near the diaphragm. The rates of grade ≥ 3 adverse events did not significantly differ between tumors near the diaphragm (4/26 sessions) and the controls (7/133 sessions) (P = 0.083). Conclusion RFA is a feasible and effective therapeutic option for lung tumors located near the diaphragm. However, it conveys a higher rate of shoulder pain and asymptomatic pleural effusion by comparison with more distant lung tumors.