Background and Purpose— Hemodynamic changes following mechanical thrombectomy for large vessel occlusion stroke could be associated with complications and might affect prognosis. We investigated postinterventional middle cerebral artery blood flow on transcranial duplex sonography (TCD) and its prognostic value for anterior large vessel occlusion stroke patients. Methods— We identified all ischemic stroke patients who had undergone mechanical thrombectomy for anterior circulation large vessel occlusion from 2010 onwards. Postinterventional middle cerebral artery flow was graded according to the sonographic Thrombolysis in Brain Ischemia score and related to patient outcome stratified by the angiographic Thrombolysis in Cerebral Infarction reperfusion status. Results— Of 215 large vessel occlusion stroke patients, 193 patients (90%) showed successful angiographic recanalization (Thrombolysis in Cerebral Infarction grade 2b-3). Of those, 69 (36%) patients had abnormal sonographic middle cerebral artery blood flow (Thrombolysis in Brain Ischemia grade 0–4) within 72 hours after mechanical thrombectomy, which was an independent predictor for poor 90-day outcome. Conclusions— TCD indicates abnormal middle cerebral artery hemodynamics in a substantial proportion of patients with angiographically defined successful mechanical thrombectomy of the anterior cerebral circulation. Such changes are associated with poor short-term outcome.