We analyzed changes in cerebral hemodynamics due to reconstructive vascular surgery using positron emission tomography (PET) in 4 patients with severe internal carotid artery (ICA) stenosis and contralateral ICA occlusion. Three patients had carotid artery stenting (CAS), while the remaining had superficial temporal artery-middle cerebral artery (STA-MCA) bypass surgery. Preoperative cerebral blood flow (CBF) studies of all patients demonstrated various decreases in CBF in a resting state and cerebral vascular reactivity (CVR) to acetazolamide (ACZ) and an increase in the oxygen extraction fraction (OEF) on both sides. These parameters improved on both sides after CAS was performed. Our results indicate that CAS performed on a stenosis contralateral to the site of occlusion will improve cerebral hemodynamics bilaterally and indirectly, patient prognosis. But further clinical trials are required to determine whether CAS significantly reduces in stroke above the occlusion.