Extracellular adenosine critically modulates ischemic brain injury, at least in part through activation of the A₁ adenosine receptor. However, the role played by the A_2A receptor has been obscured by intrinsic limitations of A_2A adenosinergic agents. To overcome these pharmacological limitations, we explored the consequences of deleting the A_2A adenosine receptor on brain damage after transient focal ischemia. Cerebral morphology, as well as vascular and physiological measures (before, during, and after ischemia) did not differ between A_2A receptor knock-out and wild-type littermates. The volume of cerebral infarction, as well as the associated neurological deficit induced by transient filament occlusion of the middle cerebral artery, were significantly attenuated in A_2A receptor knock-out mice. This neuroprotective phenotype of A_2A receptor-deficient mice was observed in different genetic backgrounds, confirming A_2A receptor disruption as its cause. Together with complimentary pharmacological studies, these data suggest that A_2A receptors play a prominent role in the development of ischemic injury within brain and demonstrate the potential for anatomical and functional neuroprotection against stroke by A_2A receptor antagonists.