Background White matter hyperintensity (WMH) has been linked to poor clinical outcomes after acute ischemic stroke. Purpose To assess whether the WMH burden on pretreatment MRI scans is associated with an increased risk for symptomatic intracranial hemorrhage (sICH) or poor functional outcome in patients with acute ischemic stroke treated with endovascular thrombectomy (EVT). Materials and Methods In this retrospective study, consecutive patients treated with EVT for anterior circulation acute ischemic stroke at a comprehensive stroke center (where MRI was the first-line pretreatment imaging strategy; January 2015 to December 2017) were included and analyzed. WMH volumes were assessed with semiautomated volumetric analysis at fluid-attenuated inversion recovery MRI by readers who were blinded to clinical data. The associations of WMH burden with sICH and 3-month functional outcome (modified Rankin Scale [mRS] score) were assessed. Results A total of 366 patients were included (mean age, 69 years ± 19 [SD]; 188 women [51%]). Median total WMH volume was 3.61 cm3 (IQR, 1.10-10.83 cm3). Patients demonstrated higher mRS scores with increasing WMH volumes (odds ratio [OR], 1.020 [95% CI: 1.003, 1.037] per 1.0-cm3 increase for each mRS point increase; P = .018) after adjustment for patient and clinical variables. There were no significant associations between WMH severity and 90-day mortality (OR, 1.007 [95% CI: 0.990, 1.024]; P = .40) or the occurrence of sICH (OR, 1.001 [95% CI: 0.978, 1.024]; P = .94). Conclusion Higher white matter hyperintensity burden was associated with increased risk for poor 3-month functional outcome after endovascular thrombectomy for large-vessel occlusive stroke. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Mossa-Basha and Zhu in this issue.