Glioblastomas are histopathologically defined by endothelial proliferation and exhibit a uniquely elevated microvessel density compared to the surrounding normal tissue from which they derive, as compared to other tumor types. Clinical efficacy of the VEGF neutralizing antibody bevacizumab (avastin) in the treatment of other solid tumors led to a pair of phase II clinical trials studying bevacizumab treatment in recurrent human glioblastomas. Encouraging results from these trials led to the accelerated FDA approval of bevacizumab in the treatment of recurrent glioblastomas. However, extended bevacizumab treatment can lead to the development of infiltrative tumor on MRI with limited neurosurgical or chemotherapy options. Future studies will be needed to be able to identify tumors that are on their way to developing this appearance before it happens, in order to effectively use new potent anti-angiogenic agents like bevacizumab in the treatment of glioblastomas or symptomatic radiation necrosis associated with glioblastomas for which bevacizumab treatment may also be effective.