Background and Purpose: We designed SITS (Safe Implementation of Treatment in Stroke) Open to determine benefit and safety of thrombectomy in clinical practice for large artery occlusion stroke, using selected stent retrievers plus standard care versus standard care alone. Methods: SITS Open was a prospective, open, blinded evaluation, international, multicenter, controlled, nonrandomized registry study. Centers lacking access to thrombectomy contributed controls. Primary end point was categorical shift in modified Rankin Scale score at 3 months in the per protocol (PP) population. Principal secondary outcomes were symptomatic intracranial hemorrhage, functional independency (modified Rankin Scale score 0–2) and death at 3 months. Patients independently evaluated by video-recorded modified Rankin Scale interviews blinded to treatment or center identity by central core laboratory were regarded as PP population. Propensity score matching with covariate adjusted analysis was performed. Results: During 2014 to 2017, 293 patients (257 thrombectomy, 36 control) from 26 centers in 10 countries fulfilled intention-to-treat and 200 (170 thrombectomy, 30 control) PP criteria; enrollment of controls was limited by rapid uptake of thrombectomy. In PP analysis, median age was 71 versus 71 years, and baseline National Institutes of Health Stroke Scale 17 versus 17 in the thrombectomy and control arms, respectively. The propensity score matching analysis for PP showed a significant shift for modified Rankin Scale at 3 months favoring the thrombectomy group (odds ratio, 3.8 [95% CI, 1.61–8.95]; P =0.002). Regarding safety, there were 4 cases of symptomatic intracranial hemorrhage in the thrombectomy group (2.4%) and none in the control group. Conclusions: In clinical practice, thrombectomy for patients with large artery occlusion stroke is superior to standard of care in our study. Registration: URL: https://www.clinicaltrials.gov . Unique Identifier: NCT02326428.