Cavernous malformations (CMs) are one of the four major types of vascular malformations of the central nervous system (CNS). Literature reports also term them cavernomas, cavernous angiomas, angiographically occult vascular malformations and cavernous hemangiomas.CMs are composed of well-circumscribed vascular channels containing blood at various stages of evolution and show a low-flow vascular pattern. They have usually been considered developmental lesions of the intracranial vasculature, but recently the de novo appearance of these malformations has been observed with increasing frequency.We describe a case of sporadic de novo formation of a CNS cavernous malformation following radiation treatment in a child with medulloblastoma. We review the patient's clinical course and the literature focusing on the role of radiation therapy in the pathogenesis of CMs.