Background: Cerebral hyperperfusion syndrome (CHS) is a failure of autoregulation after a revascularization procedure. It has rarely been reported in patients with no pre-existing cerebral hypoperfusion. Case Report: We present a rare case of a patient who underwent stent graft implantation to treat postirradiated carotid blowout syndrome. The patient developed hypertension, focal neurological deficit, and seizures after the procedure; neuroimages revealed ipsilateral cerebral edema, swelling, and increased cerebral perfusion. CHS was diagnosed based on clinical and radiological findings. The patient recovered gradually after receiving supportive care. Conclusion: Owing to the risk of CHS, monitoring for cerebral perfusion and prevention of hypertension is suggested for patients who undergo stent graft placement for postirradiated carotid blowout syndrome.