Primary retroperitoneal teratoma is a rare entity in adults. It has a distinctive imaging appearance. We describe the case of a 26-year-old man who was referred to our hospital due to an abdominal tumor. Serial work-up disclosed a teratoma at the retroperitoneum. Laparotomy with tumor resection was performed. Pathological examination revealed a mature cystic teratoma. The postoperative course was smooth. This patient was doing well at one-year follow-up.