Malignant gliomas of optic nerve and chiasm are rare, rapidly fatal neoplasms of adulthood. This report documents the occurrence of a malignant astrocytoma of the optic nerve in an 11-year-old boy who 9 years previously had a cerebellar medulloblastoma treated with surgery and irradiation. This malignant optic nerve glioma followed the same aggressive clinical course as that seen in adults, with death 9 months after diagnosis despite surgery and chemotherapy: Radiation may have been an important factor in the development of this malignant tumor which is almost never seen in the pediatric age group.