Vascular endothelial growth factors (VEGF) are a Janus-faced family of growth factors exerting both neuroprotective and maladaptive effects on the blood-brain barrier. For example, VEGFs are beneficial in promoting postischemic brain angiogenesis, but the newly formed vessels are leaky. We investigated the role of the naturally occurring murine inhibitory VEGF isoform VEGF 165b in a mouse model of focal cerebral ischemia by middle cerebral artery occlusion and reperfusion (I/R) in male C57BL/6 mice. We investigated the roles of VEGF164/165 and VEGF165b in both brain and nonbrain endothelial barrier, angiogenesis, and neutrophil migration using oxygen glucose deprivation and reoxygenation as in vitro model. We investigated the role of VEGF165b in brain edema, neutrophil infiltration, ischemic brain damage, and neuronal death in vivo using an adenovirus encoding a recombinant VEGF164b isoform. Neither VEGF164/165 nor VEGF165b significantly altered brain endothelial barrier or angiogenesis in vitro. However, treatment of brain endothelial cells with VEGF165b increased neutrophil migration in vitro and exacerbated stroke injury by aggravating neutrophil infiltration and neurodegeneration in vivo. Our results indicate that alterations in the delicate balance in the relative levels of pro- and antiangiogenic VEGF isoforms can result in either adaptive or detrimental effects, depending on the VEGF isoform levels and on the duration and extent of injury.