Intracranial atherosclerotic stenosis (IAS) remains at risk of recurrent ischemic events despite intensive medical management. Cerebrovascular reactivity (CVR) assessed by hypercapnic challenge using BOLD functional MRI (CVR BOLD fMRI) estimates cerebrovascular reserve and may allow to identify patients at higher risk of recurrent ischemic events. 19 patients referred for unilateral symptomatic IAS were studied to estimate the relationships between baseline characteristics, recurrence of ischemic events, and CVR. During follow-up, recurrent ischemic events were more frequent in patients with impaired CVR. CVR mapping may help to better select among IAS patients those at higher risk to discuss additional treatment.