BACKGROUND: Collateral circulation provides compensatory flow to ischemic brain regions in acute large vessel occlusion (LVO), which had been associated with better outcomes after endovascular treatment (EVT). AIMS: We aimed to reveal the pre-EVT collateral status and its associations with outcomes after EVT, in patients with acute LVO with different etiologies. METHODS: Based on a prospective, multicenter registry, we analyzed patients with acute, intracranial anterior-circulation LVO due to large artery atherosclerosis (LAA) and cardioembolism (CE), who underwent EVT within 24 h. Pre-EVT leptomeningeal collateral status was classified on digital subtraction angiography by ASITN/SIR grading system. Outcomes included good 3-month functional outcome (modified Rankin Scale [mRS] 0-2), 3-month mRS distribution, successful recanalization, early neurological deterioration, symptomatic intracranial hemorrhage (sICH), and 3-month mortality. RESULTS: Among 805 patients (median age 66 years), 450 and 355, respectively, had LVO due to LAA and CE, of whom 57.8% and 56.6% ( CONCLUSIONS: The study revealed comparable pre-EVT collateral status in patients with LVO due to LAA versus CE who received EVT within 24 h, but the pre-EVT collaterals may have different protective effects for post-EVT outcomes in these two groups of patients.