INTRODUCTION:: Ancient schwannoma is a rare tumor of the peripheral nerve sheath. As degenerative properties are defined histologically, it can be wrongly interpreted as malignant. CASE PRESENTATION:: The case presented here is of a giant ancient schwannoma with a pelvic retroperitoneal location, which was mimicking an adnexal mass. CONCLUSION:: In the rarely seen cases in the retroperitoneum, it may reach very large dimensions.