A fifty year old woman with no pathological history presented a well-defined, soft and painless mass located in the left iliac fossa. Abdominal ultrasound showed a mass of 18 cm in the left flank. Abdominal Computed Tomodensitography showed an heterogenous mass measuring 26cm x 22 cm, compatible with a retroperitoneal teratoma. Access was achieved through midline laparotomy. A complete surgical resection was performed. Macroscopic examination of the specimen showed a well circumscribed but non encapsulated globular mass measuring 27 x22 x 6 cm and weighing 1400 g. The cut-surface was uniform yellowish except for a whitish calcified area in the middle. No areas of hemorrhage or necrosis were seen. Histological study showed mature adipocytes arranged in lobules with vascular septa; adipocytes were indistinguishable from normal adipose tissue. Cytosteatonecrosis and calcification were seen. No mitotic activity, cellular atypia, lipoblasts or cellular invasion were observed. We used fluorescent in situ hybridization (FISH) and immunohistochemistry; there was no expression of HMB45, MDM2, and CDK4 and amplification of MDM2 and CDK4 wasn't detected. The postoperative course was simple and the patient was discharged from hospital on day 3. The patient's examination 3 months later was normal with a good clinical improvement.