Clinical trials have suggested that prehospital management in a mobile stroke unit (MSU) improves functional outcomes in patients with acute ischemic stroke who are potentially eligible for intravenous thrombolysis, but there is a paucity of real-world evidence from routine clinical practice on this topic. To determine the association between prehospital management in an MSU vs standard emergency medical services (EMS) management and the level of global disability at hospital discharge. This was a retrospective, observational, cohort study that included consecutive patients with a final diagnosis of ischemic stroke who received either prehospital management in an MSU or standard EMS management between August 1, 2018, and January 31, 2023. Follow-up ended at hospital discharge. The primary analytic cohort included those who were potentially eligible for IV thrombolysis. A separate, overlapping cohort including all patients regardless of diagnosis was also analyzed. Patient data were obtained from the American Heart Association's Get With The Guidelines-Stroke (GWTG-Stroke) Program, a nationwide, multicenter quality assurance registry. This analysis was completed in May 2024. Prehospital management in an MSU (vs standard EMS management). The primary efficacy end point was the utility-weighted modified Rankin Scale (UW-mRS) score. The secondary efficacy end point was independent ambulation status. The coprimary safety end points were symptomatic intracranial hemorrhage (sICH) and in-hospital mortality. Of 19 433 patients (median [IQR] age, 73 [62-83] years; 9867 female [50.8%]) treated at 106 hospitals, 1237 (6.4%) received prehospital management in an MSU. Prehospital management in an MSU was associated with a better score on the UW-mRS at discharge (adjusted mean difference, 0.03; 95% CI, 0.01-0.05) and a higher likelihood of independent ambulation at discharge (53.3% [468 of 878 patients] vs 48.3% [5868 of 12 148 patients]; adjusted risk ratio [aRR], 1.08; 95% CI, 1.03-1.13). There was no statistically significant difference in sICH (5.2% [57 of 1094] vs 4.2% [545 of 13 014]; aRR, 1.30; 95% CI, 0.94-1.75]) or in-hospital mortality (5.7% [70 of 1237] vs 6.2% [1121 of 18 196]; aRR, 1.03; 95% CI, 0.78-1.27) between the 2 groups. Among patients with acute ischemic stroke potentially eligible for intravenous thrombolysis, prehospital management in an MSU compared with standard EMS management was associated with a significantly lower level of global disability at hospital discharge. These findings support policy efforts to expand access to prehospital MSU management.