We present a case of thoracic splenosis in a 42-yr-old man with a medical history of abdominal surgery for a penetration injury with an iron bar of the left abdomen and back. He had been in good condition, but a chest radiograph taken during a regular checkup showed a multinodular left pleura-based mass. Computed tomography (CT) showed that the mass was well-enhanced and homogeneous, indicating a sclerosing hemangioma. Following its removal by video-assisted thoracoscopic surgery, the mass appeared similar to a hemangioma, with marked adhesion to the left side diaphragmatic pleura and lung parenchyma. Frozen section showed that the lesion was a solid mass consisted with abundant lymphoid cells, suggesting a low grade lymphoma. On permanent section, however, the mass was found to be composed of white pulp, red pulp, a thick capsule and trabeculae and was diagnosed as ectopic splenic tissue, or thoracic splenosis. Review of the patient's history and chest CT at admission revealed that the patient had undergone a splenectomy for the penetration injury 20 yr previously.