BackgroundImmune-inflammatory processes are highly associated with the progression of atherosclerosis. The systemic immune-inflammation index (SII) is a potential predictor for clinical outcomes in patients with stroke and ischemic heart disease. Therefore, this study aimed to investigate whether SII can accurately predict the short- and long-term prognoses in patients who underwent carotid artery stenting (CAS) compared to that with C-reactive protein (CRP).MethodsThis study was a single-center retrospective investigation. Overall, 129 patients who underwent CAS were categorized into tertiles based on their SII levels. We primarily investigated the long-term major adverse cardiac and cerebrovascular events (MACCE) and secondarily the in-hospital and long-term stroke incidence, as well as all-cause death.ResultsThe in-hospital stroke rate tended to increase with a rise in SII (P= 0.13). Over the 5-year follow-up period, the Kaplan–Meier overall incidence of MACCE was 9.3%, 16.3%, and 39.5% in the lowest to highest tertiles, respectively (log-rank trend test,P<0.001). The rates of stroke and MACCE during the long-term follow-up were significantly higher with increasing SII. Cox regression analysis showed that the highest tertile of SII (>647) was a predictor of the incidence of long-term stroke (hazard ratio (HR), 21.3; 95% confidence interval (CI), 2.41–188;P= 0.006) and MACCE (HR, 3.98; 95% CI, 1.80–8.81;P<0.001). However, after adjusting for both SII and CRP, only SII remained a significant independent predictor, whereas CRP became less relevant. The receiver operating characteristic curve analysis of long-term MACCE showed that the area under the curve (AUC) for SII (AUC, 0.72; 95% CI, 0.60–0.84;P<0.001) was greater than that of CRP (AUC, 0.64; 95% CI, 0.51–0.77;P= 0.040).ConclusionSII was shown to be an independent predictor of long-term prognosis in patients who underwent CAS and was suggested to be superior to CRP as an inflammatory prognosis predictor.