Teratomas are bizarre neoplasms derived from embryonic tissues that are typically found only in the gonadal and sacrococcygeal regions of adults. Primary retroperitoneal teratomas are rare and present challenging management options. We report a case of unilateral primary retroperitoneal mature cystic teratoma mimicking as an adrenal mass in 54-year-old male patient. Adrenal mass complete resection was performed by flank approach using the 11th rib resection. Because of the risk of malignancy, follow-up radiographic studies were performed to ensure the oncologic efficacy of resection. The patient has been free of recurrence for longer than 12 months.