Background: Systemic immune-inflammation index (SII) is currently considered as a potential new inflammatory marker, but its association with internal carotid artery (ICA) stenosis has been poorly studied. Therefore, the purpose of this study was to investigate whether there is a correlation between SII and the risk of stroke in patients with ICA stenosis or occlusion. Methods: A total of 302 participants (180 patients were symptomatic and 122 were asymptomatic) were enrolled in this study. Multivariate logistic regression analysis was used to determine independent risk factors for symptoms in patients with ICA stenosis. Additional subgroup analyses were performed according to degree of ICA stenosis. Results: Multivariate regression analysis showed SII (OR=1.001, 95%CI: 1.000-1.002, P=0.035) and ICA stenosis (OR=1.993, 95%CI: 1.436-2.767, P<0.001) were independently associated with symptoms in patients with ICA stenosis. Further analysis was performed using the SII quartile, with the first quartile as the reference, and the highest quartile SII level was significantly associated with symptomatic ICA (P=0.022). Trend test (P=0.004) showed a dose-response relationship between SII and the risk of symptoms in patients with ICA stenosis. In the stenosis degree analysis subgroup, SII was independently associated with symptoms in patients with severe stenosis and occlusion, while no correlation was observed in patients with moderate stenosis. Conclusions: Elevated SII levels were independently associated with symptoms in patients with ICA stenosis. Our findings suggest that SII may serve as a potential biomarker for symptomatic development in patients with severe ICA stenosis or occlusion.