OBJECTIVE: This study aimed to investigate whether and to what degree leptomeningeal collateral flow as detected on angiography influences the prognostic value of computed tomography perfusion-estimated mismatch in interventional treatment of acute anterior circulation stroke. METHODS: Thirty-eight consecutive patients with acute anterior circulation stroke who received interventional neuroradiologic treatment were assigned one of 2 groups depending on the patient's degree of collateral flow (18 patients with poor collaterals, 20 patients with high degree collaterals) according to the American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology grading system. In a multiregression model, we investigated a possible interaction between 2 independent variables mismatch ratio and degree of collateral flow using a "centered" variable approach. RESULTS: The mismatch ratio per se showed a significant correlation with final clinical outcome (β coefficient, -0.79; P = 0.02); whereas, there was no interaction shown between mismatch degree of collateral flow (β coefficient, 0.54; P = 0.1). CONCLUSIONS: This study suggests that the predictive value of computed tomography perfusion-estimated mismatch is not influenced by the degree of leptomeningeal collateral flow.