Schwannomas are nerve sheath tumors that seldom occur in the retroperitoneal region. Herein, we describe an incidentally detected retroperitoneal schwannoma that mimicked liquefied hematoma on computed tomography. A 61-year-old man was admitted to the emergency department with chest pain caused by a fall at a construction site. Chest computed tomography incidentally revealed a retroperitoneal cystic mass measuring 10 cm, in addition to multiple rib fractures and hemopneumothorax. The patient frequently consumed alcohol and had a history of repeated trauma; therefore, we considered the following 2 conditions: retroperitoneal cystic tumor and liquefied hematoma. He underwent complete surgical excision, and a histopathological examination confirmed the mass as a schwannoma. Experience and knowledge regarding the computed tomography findings of retroperitoneal cystic schwannoma are useful for the differential diagnosis of infrequent retroperitoneal tumors.