Background: Bleeding of the subclavian artery is a fatal condition. Adhesion between the pleura and staple line may develop after surgical treatment of pneumothorax, and collateral arteries often develop from the subclavian artery toward the adhesion at the lung apex; however, atraumatic tearing and bleeding of these collateral arteries into the extrapleural and intrathoracic cavities is rare. Case presentation: A 70-year-old man visited the hospital for evaluation of left chest pain. Contrast-enhanced chest computed tomography showed a huge tumor in the left apex of the lung. It was suspected to be an extrapleural huge hematoma, and it ruptured into the thoracic cavity. Bleeding from the left subclavian artery was suspected; therefore, emergency angiography was performed. Angiography showed some collateral circulation from the left subclavian artery to the apex of the left lung. Distal and proximal bleeding points were identified. The distal bleeding point was embolized using coils. The proximal bleeding point was blown out, and stents were placed in the left subclavian artery. He had undergone pneumothorax surgery 20 years previously, and the present bleeding episode was strongly suspected to be associated with that surgery. The collateral circulation from the subclavian artery could have developed because of post-pneumothorax inflammation, eventually rupturing and bleeding into the extrapleural space. Conclusions: This report described an important case of atraumatic subclavian artery bleeding considered to have been caused by surgical treatment of pneumothorax 20 years previously. Emergency angiography and percutaneous stent placement or coil embolization should be considered first in such cases.