Background: The IMS-III trial was terminated early for futility after interim analysis showed no difference between intraarterial (IA) and intravenous (IV) treatment arms. This analysis is an attempt to understand the occurrence and predictors of futile recanalization in the IMS-III. Materials and methods: Data of IMS-III patients were treated with IA intervention was analyzed. Patients with near complete or complete recanalization (thrombolysis in cerebral infarction [TICI] gradesIIband III) were selected then divided, according to functional outcome at 3 months into “useful recanalization” - defined as modified Rankin scale (mRS) 0-2 and “futile recanalization” -mRS 3-6. Subjects with symptomatic intracerebral hemorrhage (ICH), posterior circulation occlusion, or missed data were excluded. Univariate analysis was performed to examine the differences between the two groups. Logistic regression was performed to identify the predictors of futility. Variables selected for the logistic regression are those significant in the univariate analysis. Results: Complete or near complete recanalization was observed in 145 of 434 patients treated with IA. Only 118 met the criteria for this analysis. Of those, 71 (60%) patients had useful recanalization and 47 (40%) had futile recanalization.Compared to patients with useful recanalization, patients with futile recanalization had higher incidence of diabetes mellitus, higher median baseline NIHSS scores (19 vs 15, p<0.001), higher median ASPECTS; 8 vs 7, longer time from onset to IV tPA (131 vs 116 min, p=0.026), longer time from onset to IA therapy (267vs 240 min, p=0.010), longer hospital stay (13±9vs 6±4 days, p<0.001), and a non-significant trend towards higher mortality rate (1.4% vs 10.6%, p=0.07). In logistic regression analysis,the only independent predictor of futile recanalization was baseline NIHSS≥20 (odds ratio, 4.1; 95% confidence interval, 1.1-16.4, p=0.043), while female gender, time to IV tPA, and ASPECTS showed a non significant trend. Conclusions: Futile recanalization is a relatively common following IA treatment in the IMS-III trial. Important clinical factors can predict this phenomenon, which is associated with high resources utilization without functional benefit.