An ancient schwannoma is a rare variant of schwannoma characterized by degenerative changes and diffuse hypocellularity. Because a retroperitoneal schwannoma is usually asymptomatic, the diagnosis is often casual and difficult to determine preoperatively. Magnetic resonance imaging is the most valuable radiologic technique for its evaluation. The treatment of choice is complete surgical excision. Herein, we report a case of retroperitoneal ancient schwannoma in a 52-year-old woman presenting with an incidentally found retroperitoneal tumor. The patient has no evidence of disease 6 months after the surgery.