Cerebral cavernous malformations (CCM) are known to occur in both sporadic and familial forms. To date, there has been no identified association of CCM with glioblastoma multiforme. We present a 69-year-old woman with a 14 year history of multiple CCM who developed progressive aphasia. She had no radiation exposure and had only undergone a single computed tomography scan in her entire life. MRI demonstrated irregular gadolinium enhancement in the area of a prior stable CCM, suspicious for a high grade tumor. Stereotactic biopsy revealed a glioblastoma multiforme. This is a unique case of glioblastoma multiforme arising from the "site" of a known CCM. We review the literature on the genetics of cavernous malformations and propose a mechanism for the tumorigenic potential of these vascular malformations.