Get With The Guidelines (GWTG)-Stroke is a national, hospital-based quality improvement program developed by the American Heart Association. Although studies have suggested improved processes of care in GWTG-Stroke-participating hospitals, it is not known whether this improved care translates into improved clinical outcomes compared with nonparticipating hospitals.From all acute care US hospitals caring for Medicare beneficiaries with acute stroke between April 2003 and December 2008, we matched hospitals that joined the GWTG-Stroke program with similar hospitals that did not. Using a difference-in-differences design, we analyzed whether hospital participation in GWTG-Stroke was associated with a greater improvement in clinical outcomes compared with the underlying secular change.The matching algorithm identified 366 GWTG-Stroke-adopting hospitals that cared for 88 584 acute ischemic stroke admissions and 366 non-GWTG-Stroke hospitals that cared for 85 401 acute ischemic stroke admissions. Compared with the Pre period (18-6 months before program implementation), in the Early period (0-6 months after program implementation), GWTG-Stroke hospitals had accelerated increases in discharge to home and reduced mortality at 30 days and 1 year. In the Sustained period (6-18 months after program implementation), the accelerated reduction in mortality at 1 year was sustained, with a trend toward sustained accelerated increase in discharge home.Hospital adoption of the GWTG-Stroke program was associated with improved functional outcomes at discharge and reduced postdischarge mortality.