Background and Purpose— Vascular endothelial growth factor (VEGF) expression is elevated in human brain arteriovenous malformations (bAVM). We have developed a bAVM model in the adult mouse by focal Alk1 gene deletion and human VEGF stimulation. We hypothesized that once the abnormal vasculature has been established, tonic VEGF stimulation is necessary to maintain the abnormal phenotype, and VEGF antagonism by bevacizumab (Avastin) would reduce vessel density and attenuate the dysplastic vascular phenotype. Methods— Angiogenesis and bAVM were induced by injection of adeno-associated viral vector expressing human VEGF alone into the brain of wild-type mice or with adenoviral vector expressing Cre recombinase (Ad-Cre) into Alk1 2f/2f mice. Six weeks later, bevacizumab or trastuzumab (Herceptin, bevacizumab control) was administered. Vessel density, dysplasia index, vascular cell proliferation and apoptosis, and human IgG were assessed (n=6/group). Results— Compared with trastuzumab (15 mg/kg), administration of 5, 10, and 15 mg/kg of bevacizumab to adeno-associated viral vector expressing human VEGF treated wild-type mice reduced focal vessel density ( P <0.05); administration of 5 mg/kg bevacizumab decreased proliferating vascular cells ( P =0.04) and increased TUNEL-positive vascular cells ( P =0.03). More importantly, bevacizumab (5 mg/kg) treatment reduced both vessel density ( P =0.01) and dysplasia index ( P =0.02) in our bAVM model. Human IgG was detected in the vessel wall and in the parenchyma in the angiogenic foci of bevacizumab-treated mice. Conclusions— We provide proof-of-principle that, once abnormal AVM vessels have formed, VEGF antagonism may reduce the number of dysplastic vessels and should be evaluated further as a therapeutic strategy for the human disease.