Intrathoracic gossypiboma, a retained surgical sponge in the thoracic cavity, is a rare but serious complication of thoracic surgeries. A 70-year-old man presented with an eight-month history of cough. He had undergone coronary artery bypass surgery eight years ago. The posteroanterior chest X-ray revealed a well-marginated homogeneous opacity at the left hemithorax with striped appearance in the center. Thoracic CT revealed a pleural-based mass at the left lower lobe with a hyperdense rim. After the diagnosis of gossypiboma, it was removed surgically. Although rare after thoracic surgery, gossypibomas need to be considered in the differential diagnosis in case of respiratory symptoms.