Background and Purpose: This study investigates clinical outcomes after mechanical thrombectomy in adult patients with baseline Alberta Stroke Program Early CT Score (ASPECTS) of 0 to 5. Methods: We included data from the STRATIS Registry (Systematic Evaluation of Patients Treated With Neurothrombectomy Devices for Acute Ischemic Stroke) from patients who underwent mechanical thrombectomy within 8 hours of symptom onset and had available ASPECTS data adjudicated by an independent core laboratory. Angiographic and clinical outcomes were collected, including successful reperfusion (modified Thrombolysis in Cerebral Infarction ≥2b), functional independence (modified Rankin Scale score 0–2), 90-day mortality, and symptomatic intracranial hemorrhage at 24 hours. Outcomes were stratified by ASPECTS scores and age. Results: Of the 984 patients enrolled, 763 had available ASPECTS data. Of these patients, 57 had ASPECTS of 0 to 5 with a median age of 63 years (interquartile range, 28–100), whereas 706 patients had ASPECTS of 6 to 10 with a median age of 70 years of age (interquartile range, 19–100). Ten patients had ASPECTS of 0 to 3 and 47 patients had ASPECTS of 4 to 5 at baseline. Successful reperfusion was achieved in 85.5% (47/55) in the ASPECTS of 0 to 5 group. Functional independence was achieved in 28.8% (15/52) in the ASPECTS of 0 to 5 versus 59.7% (388/650) in the 6 to 10 group ( P <0.001). Mortality rates were 30.8% (16/52) in the ASPECTS of 0 to 5 and 13.4% (87/650) in the 6 to 10 group ( P <0.001). sICH rates were 7.0% (4/57) in the ASPECTS of 0 to 5 and 0.9% (6/682) in the 6 to 10 group ( P <0.001). No patients aged >75 years with ASPECTS of 0 to 5 (0/12) achieved functional independence versus 44.8% (13/29) of those age ≤65 ( P =0.005). Conclusions: Patients <65 years of age with large core infarction (ASPECTS 0–5) have better rates of functional independence and lower rates of mortality compared with patients >75 years of age. Registration: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT02239640.