Neurofibromatosis type 1 is a common multisystemic disorder that can result in tumors of the central and peripheral nervous system. Individuals with neurofibromatosis type 1 are also at increased risk to develop moyamoya syndrome, which is a cerebrovascular condition that predisposes affected individuals to develop strokes as a result of progressive narrowing of the intracranial internal carotid arteries and failure of adequate blood supply through collateral vessels. We report a case of a young boy with neurofibromatosis type 1 with glioblastoma who developed rapidly progressive moyamoya vasculopathy after treatment with the angiogenesis inhibitor bevacizumab.