Thoracic splenosis is a rare disease that develops as a result of autotransplantation of splenic tissue into the thoracic cavity following splenic and diaphragmatic injury. We report the case of a 53-year-old man with a chief complaint of heartburn and cough. He had a history of traumatic diaphragmatic rupture treated with surgical repair and splenectomy 15 years ago. Imaging studies revealed a paraesophageal mass, and surgical resection was performed considering the possibility of Castleman disease or an esophageal submucosal tumor. Pathologic results showed findings of normal splenic tissue. The patient was discharged on postoperative day 5 without any complications.