The isolated retroperitoneal malignant schwannoma unassociated with Von Recklinghausen's disease is an unusual neoplasm, representing 0.01% of all retroperitoneal malignant neoplasms, with a poor prognosis, and an average survival at 5 years of 50% in patients treated by radical exeresis. At present, it is impossible, without histologic and immunohistochemical examinations, to differentiate it from other isolated retroperitoneal sarcomatous neoplasms. The authors report a case of retroperitoneal malignant schwannoma 20 cm in diameter in a 62-year-old woman surgically treated by radical exeresis. Postoperative complications were absent, and the patient, discharged from the hospital on the 12th postoperative day, died 8 months later of diffuse metastases, without local relapse. Despite the patient's short survival, the authors believe radical surgery to be the best therapeutic choice. Only surgery can establish a final diagnosis and can offer the best chance of survival and a significant and sometimes prolonged relief of symptomatology.