BACKGROUND Splenosis refers to autotransplantation of splenic tissue after splenic injury or splenectomy, most frequently occurring in the abdominal and pelvic cavities. Thoracic splenosis is a rare condition associated with a history of simultaneous rupture of the spleen and diaphragm resulting from trauma. To the best of our knowledge, only a limited number of cases have been reported for combined intrathoracic and abdominal splenosis. CASE REPORT We present a case of a 50-year-old man with a history of splenectomy and left nephrectomy 15 years ago due to an accident, who had experienced chest pain for the past month. A 1-cm focal pleural thickening in the left posterior pleura was revealed on the chest computed tomography (CT) scan. We found this to be suspicious for a solitary fibrous tumor. Based on this information, surgery was performed for tumor removal, and the pathologic examination confirmed splenic tissues. The patient was then discharged without any complications. Further abdominopelvic CT showed several contrast-enhanced lesions, suggestive of intraperitoneal splenosis. CONCLUSIONS We would like to emphasize the importance of thorough history-taking to avoid misdiagnosis and unnecessary procedures with respect to the rarity of splenosis. Moreover, appropriate use of diagnostic tools, including radionuclide imaging studies, is recommended to establish an accurate diagnosis of thoracic splenosis.