Primary teratomas in the retroperitoneum are rare in adults. Most teratomas in this region are secondary to germ cell tumors of the testes or ovaries. We describe a case of mature cystic teratoma that was clinically suggestive of an adrenal myelolipoma. Resection was attempted using laparoscopy but was converted to open adrenalectomy to ensure complete 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 18 months.