['Pretreatment infarct volume appears to predict clinical outcome after intra-arterial therapy. To confirm the importance of infarct size in patients undergoing intra-arterial therapy, we sought to characterize the relationship between final infarct volume (FIV) and long-term functional outcome in a prospective cohort of endovascularly treated patients.', 'From our prospective intra-arterial therapy database, we identified 107 patients with acute ischemic stroke with anterior circulation proximal artery occlusions who underwent final infarct imaging and had 3-month modified Rankin Scale scores. Clinical, imaging, treatment, and outcome data were analyzed.', 'Mean age was 66.6 years. Median admission National Institutes of Health Stroke Scale score was 17. Reperfusion (Thrombolysis In Cerebral Infarction 2A-3) was achieved in 78 (72.9%) patients. Twenty-seven (25.2%) patients achieved a 3-month good outcome (modified Rankin Scale 0-2), and 30 (28.0%) died. Median FIV was 71.4 cm(3). FIV independently correlated with functional outcome across the entire modified Rankin Scale. In receiver operating characteristic analysis, it was the best discriminator of both good outcome (area under the curve=0.857) and mortality (area under the curve=0.772). A FIV of approximately 50 cm(3) demonstrated the greatest accuracy for distinguishing good versus poor outcome, and a FIV of approximately 90 cm(3) was highly specific for a poor outcome. The interaction term between FIV and age was the only independent predictor of good outcome (P<0.0001). The impact of FIV was accentuated in patients <80 years.'] Is infarct volume a pivotal biomarker after intra-arterial stroke therapy?