Objective:To investigate the correlation between collateral circulation and infarct pattern and outcome in acute ischemic stroke patients with anterior circulation intracranial atherosclerosis.Methods:Acute ischemic stroke patients with anterior circulation intracranial atherosclerotic severe stenosis or occlusion admitted to the Department of Neurology, the First Affiliated Hospital of Xinxiang Medical College from September 2018 to March 2020 were included prospectively. According to diffusion-weighted imaging, the infarct patterns were divided into perforator pattern, territorial pattern, watershed pattern, and mixed pattern. At 90 d after onset, the modified Rankin Scale was used to evaluate the outcome. 0-2 was defined as good outcome, and >2 was defined as poor outcome. Multivariate logistic regression analysis was used to determine the independent influencing factors of clinical outcome. Results:A total of 89 patients were enrolled, 50 (56.2%) had good collateral circulation and 39 (43.8%) had poor collateral circulation. The distribution patterns of infarct: 22 patients (24.7%) were perforator pattern, 26 (29.2%) were territorial pattern, 17 (19.1%) were watershed pattern, and 24 (30.0%) were mixed pattern. The proportion of patients with good collateral circulation was 81.8%, 65.4%, 29.4% and 41.7%, respectively in the perforator pattern group, territorial pattern group, watershed pattern group, and mixed pattern group. Good collateral circulation was more common in the perforator pattern group, and poor collateral circulation was more common in the watershed pattern group. At 90 d after onset, 53 patients (59.6%) had a good outcome and 36 (40.4%) had a poor outcome. The baseline homocysteine level in the good outcome group was significantly lower than that in the poor outcome group (17.91±4.62 μmol/L vs. 20.35±4.67 μmol/L; t=2.436, P=0.017), and the proportion of patients with good collateral circulation was significantly higher than that of patients with poor outcome (73.6% vs. 30.6%; χ2=16.124, P<0.001). Multivariate logistic regression analysis showed that higher homocysteine level was an independent risk factor for poor outcome (odds ratio 1.174, 95% confidence interval 1.061-1.298; P=0.002) and good collateral circulation was an independent protective factor for good outcome (odds ratio 0.095, 95% confidence interval 0.038-0.239; P<0.001). Conclusions:Good collateral circulation was more common in patients with perforator pattern, and poor collateral circulation was more common in patients with watershed pattern. Good collateral circulation was independently associated with the good clinical outcome in acute ischemic stroke patients with anterior circulation intracranial atherosclerosis.