Internal carotid artery stenosis is an established risk factor for stroke. Therefore, carotid artery revascularization has an important role in the prevention and treatment of stroke. For the treatment of carotid artery stenosis, carotid artery stenting (CAS) has currently gained acceptance as a safe alternative to carotid endarterectomy (CEA), particularly in patients at high surgical risk. Duplex ultrasonography (DUS) is a non-invasive technique with standardized criteria used for the diagnosis of carotid atheromatous disease as well as for the detection of restenosis after carotid revascularization. Restenosis rates vary widely in the literature. Different studies indicated that restenosis following CAS was higher than following CEA, although the Carotid Revascularization Endarterectomy Versus Stenting Trial (CREST) reported similar restenosis frequency after 2 years of follow-up. Given these results, DUS may have a significant role in the follow-up of CAS patients. Conventional carotid artery DUS velocity criteria are thought to be less accurate in patients who have undergone CAS and many authors proposed different criteria for grading in-stent restenosis (ISR). This review presents the advantages of CAS, the current practice of carotid revascularization, CAS complications and risks, and DUS criteria for carotid artery ISR. After analyzing multiple relevant studies that proposed sonographic criteria for grading at least 70% ISR, we can conclude that a peak systolic velocity value of 300-350 cm/s could be used as a relatively good and sensitive predictor of high grade ISR.