One hundred and sixty-five cases of malignant schwannoma were reviewed. Sixty-five (40%) of the patients had evidence of disseminated neurofibromatosis. Patients with neurofibromatosis were younger, had malignant schwannomas that were centrally rather than peripherally located, and had a shorter five-year survival (23%) than patients with solitary malignant schwannomas (47%). Histologically, tumors developing in patients with neurofibromatosis had a collagenous appearance, while tumors in patients without neurofibromatosis were undifferentiated and highly cellular. The clinical course of both groups of patients tended to be that of multiple local recurrences, although local recurrence had a more ominous prognosis in patients with neurofibromatosis. Chemotherapy responses in all these patients were extremely poor; however, the results of adjuvant therapy after surgery appeared encouraging. Fourteen patients (8.5%) had a malignant schwannoma in an area of prior radiation therapy and died of disease a median of 14 months after diagnosis. Malignant schwannoma should be considered in the differential diagnosis of tumors developing in areas previously treated with radiation.