Thoracic splenosis refers to a condition of ectopic splenic tissue in the thoracic cavity. It is usually a consequence of splenic tissue seeding in the pleural cavity after thoracoabdominal trauma. A rare case of thoracic splenosis, in a 62-year-old man who had had a traumatic splenectomy due to thoracoabdominal trauma 29 years earlier, is reported. The patient, a heavy smoker, was admitted for evaluation of a left-side thoracic lesion discovered on a plain chest film. Bronchoscopy, CT scan and needle biopsy proved inconclusive for the diagnosis. Exploratory thoracotomy was necessary to establish the diagnosis. During the operation, a thoracic splenosis was confirmed. To date, only 28 cases of thoracic splenosis have been reported in the literature. The purpose of this report is to present a new case of splenosis of the thoracic cavity simulating intrathoracic neoplasm.