Summary: Ancient schwannoma, is a rare variant of schwannoma with characterization of degenerative changes and diffuse hypercellularity. Retroperitoneal presacral form is often found incidentally, because they present with vague symptoms or symptomless. Schwannoma occurring in this area occasionally presents with enormous dimensions, known as a giant schwannoma. The tumor removal is a surgical challenge due to the difficult approach and abundant vascularity. In this report we describe a 61 –year old female presented to ER with vaginal bleeding and lower abdominal pain. The case diagnosed on clinical, CT and MRI findings to be a fibroma of the left ovary. Exploration by the gynecology team revealed a huge retroperitoneal presacral tumor compressing the left external iliac vessels and displacing the left ureter; they took a biopsy and closed the abdomen. Histopathological result was benign schwannoma. The patient were referred to our hospital (Al Hada Armed Forces Hospital, Taif, Saudi Arabia) to be managed from postoperative DVT when her family asked our department of surgery for further management and signed a high risk consent. We explored the case after insertion of IVC filter and ureteric catheter. A 20x20 cm mass was thoroughly dissected and resected with part of sacrum. The final histopathological result was benign nerve sheath tumor with features consistent with degenerated (ancient) schwannoma and the tumor was completely resected. The patient was discharged from the hospital without complications and follow up for three years revealed no recurrence.The clinical, radiological, and pathological features of this disease are discussed in this report. To conclude, retroperitoneal giant ancient schwannomas are a rare variant of the benign schwannoma and often present as unrecognized slow growing masses. Keep in mind potentially severe bleeding and neurological deficit risk of surgical intervention without away from oncologic principle. Therefore, careful preoperative evaluations and postoperative monitoring are necessary.