In the absence of systematic immunohistochemistry investigations, only 25 cases (out of 69) clearly diagnosed as neurosarcoma due to the association with Von Recklinghausen disease (ie, neurofibromatosis type 1) and treated at the Institut Gustave Roussy were included in the present study. Neurosarcoma consists of a neurocristopathy whose cells migrate to several parts of the body in order to constitute neuroglia, Schwann cells, pigmented and endocrinal tissues. From 1967 to 1990, 25 cases of such neurosarcomas associated with a neurofibromatosis type 1 were seen at our institute. Three different histological terms exist for this tumour: malignant schwannoma, neurosarcoma, and more recently, malignant peripheral nerve sheath tumours (MPNST). The median age (23 years) of the patients with neurofibromatosis type 1 is lower than that of patient with isolated neurosarcoma. Their sex ratio is 2/1. Primary tumour surgical exeresis was performed in all cases, with poor results in 7. Post-operative radiation therapy was not systematically used in this series. It was administered only in cases with incomplete surgical exeresis or when a local recurrence occurred. Adjuvant CYVADIC (doxorubicin, procarbazine, cyclophosphamide, vincristine) chemotherapy was administered in 5 cases, of in cases of relapse (8). All cases but 2 (the most recent ones) relapsed within 1 to 226 months (median 7 months). In addition, 13 patients developed metastases. Overall, the 2-year and 4-year survival rates were 41% and 18%, respectively. Our observations confirm the very poor prognosis for the association of neurofibromatosis type 1 and neurosarcoma. This finding should lead to systematically associate radical surgical exeresis, post-operative irradiation and adjuvant chemotherapy in the treatment of these patients.