Background and Purpose— A direct aspiration first pass technique (ADAPT) has been reported to be fast, safe, and effective for the treatment of acute ischemic stroke. The aim of this study is to determine the preoperative factors that affect success of the aspiration component of the technique in ischemic stroke patients with large vessel occlusion in the anterior circulation. Methods— We enrolled all 347 consecutive patients with anterior circulation acute ischemic stroke admitted for mechanical thrombectomy at our institution from August 2013 to October 2015 and treated by ADAPT for the endovascular treatment of stroke. Baseline and procedural characteristics, modified thrombolysis in cerebral infarction scores, and 3-month modified Rankin Scale were captured and analyzed. Results— Among the 347 patients (occlusion sites: middle cerebral artery=200, 58%; internal carotid artery Siphon=89, 25%; Tandem=58, 17%), aspiration component led to successful reperfusion (modified thrombolysis in cerebral infarction 2b/3 scores) in 55.6% (193/347 patients), stent retrievers were required in 40%, and a total successful final reperfusion rate of 83% (288/347) was achieved. Overall, procedural complications occurred in 13.3% of patients (48/347). Modified Rankin Scale score of 0 to 2 at 90 days was reported in 45% (144/323). Only 2 factors positively influenced the success of the aspiration component: an isolated middle cerebral artery occlusion ( P <0.001) and a shorter time from stroke onset to clot contact ( P =0.018). Conclusions— In this large retrospective study, ADAPT was shown to be safe and effective for anterior circulation acute ischemic stroke with a final successful reperfusion achieved in 83%. The site of arterial occlusion and delay of the procedure were predictors for reperfusion. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT02523261, NCT02678169, and NCT02466893.