Primary retroperitoneal mucinous cystadenomas (PRMC) are rare benign neoplasms with only 55 documented cases in the English literature so far. A 19-year-old female exhibited hirsutism and was found to have a cystic mass measuring 5.8 cm x 3.9 cm x 5.8 cm in the left retroperitoneum. During subsequent work up, a high pre-operative value of dehydroepiandrosterone sulfate (DHEA-S) was noted. The patient was referred to surgical oncology and underwent an uneventful laparoscopic cystectomy. Pathology classified the cyst as PRMC. Post-operatively, the patient's DHEA-S levels normalized, though there was no appreciable decrease in the patient's hirsutism in the short-term follow-up. The origin of PRMC is uncertain. Due to their unknown biological potential, surgical resection is usually recommended. To the best of our knowledge, this is the first report documenting a PRMC and elevated levels of androgens in conjunction with hirsutism.