Two liver tumors undetected by ultrasonography (US) because they were located in the hepatic dome were treated with radiofrequency (RF) ablation therapy after intrathoracic saline solution infusion. After administration of local anesthesia, artificial pneumothorax was produced by needle thoracentesis and a drainage catheter was inserted into the right thoracic cavity. After saline solution (450-500 mL) was injected into the thoracic cavity via the catheter, US-guided RF ablation was performed. No severe complications occurred and complete therapeutic effects were obtained. Percutaneous RF ablation therapy with intrathoracic saline solution injection seems to be a feasible alternative to other ablation therapies.