We report the case of a 64-year-old man who underwent percutaneous computed tomography(CT)-guided lung biopsy for a slow-growing lung mass at segment 6 of the left lobe.The patient developed a massive hemothorax due to bleeding from the pulmonary artery during the procedure;subsequent embolization with N-butyl cyanoacrylate(NBCA)was successful to arrest the bleeding.We believe that this is the first report in the literature of massive hemothorax from the pulmonary artery.Introduction Percutaneous CT-guided lung biopsy is a widely accepted technique for the diagnosis of lung lesions.However,there are several complications associated with this procedure(1-3).Pneumothorax is the most frequent,followed by bleeding(4),including asymptomatic parenchymal bleeding,hemoptysis,and hemothorax.Bleeding that causes hemothorax results mainly from injury to a bronchial artery,arteries in the chest wall,such as the intercostal or internal thoracic artery,and the phrenic artery(5).Although injuring the pulmonary artery may potentially cause bleeding into the thoracic cavity,to our knowledge,hemothorax from the pulmonary artery has not been reported previously.We herein report a case in which a massive hemothorax because of bleeding from the pulmonary artery occurred after percutaneous CT-guided lung biopsy.Subsequent embolization with N-butyl cyanoacrylate(NBCA)was successful to arrest the bleeding.