BACKGROUND AND PURPOSE: Although recanalization is the goal of thrombolysis, it is well recognized that it fails to improve outcome of acute stroke in a subset of patients. Our aim was to assess the rate of and factors associated with "futile recanalization," defined by absence of clinical benefit from recanalization, following endovascular treatment of acute ischemic stroke. MATERIALS AND METHODS: Data from 6 studies of acute ischemic stroke treated with mechanical and/or pharmacologic endovascular treatment were analyzed. "Futile recanalization" was defined by the occurrence of unfavorable outcome (mRS score of ≥3 at 1-3 months) despite complete angiographic recanalization (Qureshi grade 0 or TIMI grade 3). RESULTS: Complete recanalization was observed in 96 of 270 patients treated with IA thrombolysis. Futile recanalization was observed in 47 (49%). In univariate analysis, patients with futile recanalization were older (73 ± 11 versus 58 ± 15 years, P < .0001) and had higher median initial NIHSS scores (19 versus 14, P < .0001), more frequent BA occlusion (17% versus 4%, P = .049), less frequent MCA occlusion (53% versus 76%, P = .032), and a nonsignificantly higher rate of symptomatic hemorrhagic complications (2% versus 9%, P = .2). In logistic regression analysis, futile recanalization was positively associated with age >70 years (OR, 4.4; 95% CI, 1.9 -10.5; P = .0008) and initial NIHSS score 10-19 (OR, 3.8; 95% CI, 1.7- 8.4; P = .001), and initial NIHSS score ≥20 (OR, 64.4; 95% CI, 28.8-144; P < .0001). CONCLUSIONS: Futile recanalization is a relatively common occurrence following endovascular treatment, particularly among elderly patients and those with severe neurologic deficits.