Malignant retroperitoneal schwannoma is an extremely rare tumor, with only six cases previously reported occurring in the perirenal space. We herein report the seventh case. A 50-year-old woman presented with an abdominal mass suggestive of renal cell carcinoma by standard preoperative evaluation. The tumor required surgical exploration and pathologic evaluation for diagnosis. The final histologic diagnosis was made with the aid of electron microscopy and immunohistochemical staining with antibodies for S-100 protein.