Objective:To investigate the effect of regional leptomeningeal collateral circulation (rLMC) score based on CT angiography (CTA) and onset-to-reperfusion time (OTR) on the outcome after endovascular treatment (EVT) in patients with anterior circulation acute large vessel occlusive stroke (ACA-LVOS).Methods:Patients with ACA-LVOS underwent EVT in the Department of Neurology, the Affiliated Hospital of Yangzhou University from July 2017 to July 2023 were included retrospectively. The rLMC score 0-10 was defined as poor collateral circulation, and 11-20 were defined as good collateral circulation. At 90 days after EVT, the modified Rankin Scale (mRS) was used to evaluate the outcome. A score of 0-2 was defined as a good outcome and 3-6 were defined as a poor outcome. Multivariate logistic regression analysis was used to determine the independent influencing factors of the outcome after EVT. Results:A total of 144 patients with ACA-LVOS underwent EVT were enrolled, including 78 males (54.2%), median aged 73 years. The median baseline National Institutes of Health Stroke Scale (NIHSS) score was 16, the median baseline Alberta Stroke Program Early CT Score (ASPECTS) was 9, and the median OTR was 330.5 minutes. Eighty patients (55.6%) had good collateral circulation, 63 (43.8%) had poor outcome, including 13 deaths. Univariate analysis showed that there were significant differences in hypertension, previous stroke history, smoking, triglycerides, baseline NIHSS score, baseline ASPECTS, OTR, and collateral circulation status between the good outcome group and the poor outcome group (all P<0.05). Multivariate logistic regression analysis showed that good collateral circulation (odds ratio [ OR] 0.223, 95% confidence interval [ CI] 0.077-0.643; P=0.005) was an independent predictor of good outcome. In the poor collateral circulation group, longer OTR was an independent predictor of poor outcome ( OR 1.020, 95% CI 1.008-1.032; P=0.001). In the good collateral circulation group, longer OTR was not an independent risk factor for poor outcome ( OR 1.005, 95% CI 1.000-1.010; P=0.062). Conclusion:rLMC score based on CTA and OTR are the independent predictors of the outcome after EVT in patients with ACA-LVOS.