© 2017 American Medical Association. IMPORTANCE Mechanical thrombectomy (MT) improves clinical outcomes in patients with acute ischemic stroke (AIS) caused by a large vessel occlusion. However, it is not known whether intravenous thrombolysis (IVT) is of added benefit in patients undergoingMT. OBJECTIVE To examine whether treatment with IVT before MT with a stent retriever is beneficial in patients undergoingMT. DESIGN, SETTING, AND PARTICIPANTS This post hoc analysis used data from 291 patients treated with MT included in 2 large, multicenter, prospective clinical trials that evaluated MT for AIS (Solitaire With the Intention for Thrombectomy performed from January 1, 2010, through December 31, 2011, and Solitaire Flow Restoration Thrombectomy for Acute Revascularization from January 1, 2010, through December 31, 2012). An independent core laboratory scored the radiologic outcomes in each trial. INTERVENTIONS Patients were treated with IVT with tissue plasminogen activator followed by MT (IVT and MT group) with the use of a stent retriever orMT with a stent retriever alone (MT group). MAIN OUTCOMES AND MEASURES Successful reperfusion, functional independence (modified Rankin Scale score of 0-2) and mortality at 90 days, symptomatic intracranial hemorrhage, emboli to new territory, and vasospasm were compared. RESULTS Of 291 patients included in the analysis, 160 (55.0%) underwent IVT and MT (mean [SD] age, 67  years; 97 female [60.6%]), and 131 (45.0%) underwent MT alone (mean [SD] age, 69  years; 71 [55.7%] female). Median Alberta Stroke Program Early CT Score at baseline was lower in the IVT and MT group (8 vs 9, P = .04). There was no statistically significant difference in the duration from symptom onset to groin puncture (254 minutes for the IVT and MT group vs 262 minutes for the MT group, P = .10). The number of passes, rate of successful reperfusion, functional independence at 90 days, mortality at 90 days, and emboli to new territory were also similar among groups. Symptomatic intracranial hemorrhage (1% vs 4%) and parenchymal hemorrhages type 1 (1% vs 3%) or type 2 (1% vs 2%) did not differ significantly (P = .25). Vasospasm occurred more often in patients who received IVT and MT vs MT alone (27%vs 14%, P = .006). In multivariate analysis, no statistically significant association was observed between IVT and MT vs MT alone for any of the outcomes. CONCLUSIONS AND RELEVANCE The results indicate that treatment of patients experiencing AIS due to a large vessel occlusion with IVT before MT does not appear to provide a clinical benefit overMT alone. A randomized clinical trial seems warranted.