BACKGROUND: Efforts to improve prescription of oral anticoagulation (OAC) drugs in patients with atrial fibrillation have had limited success in improving guideline adherence. METHODS: We evaluated adherence to the American College of Cardiology/American Heart Association performance measures for OAC in eligible patients with a CHA2DS2-VASc score ≥2 and trends in prescription over time in the American Heart Association's Get With The Guidelines-AFIB (atrial fibrillation) registry. Adjusted associations with in-hospital outcomes were also determined. The cohort included 33 235 patients with a CHA2DS2-VASc score ≥2 who were admitted for atrial fibrillation and were enrolled at 115 sites between January 1, 2013, and September 31, 2017. RESULTS: The median (25th, 75th percentile) age was 73 years (65, 81 years); 51% were female; and the median (25th, 75th percentile) CHA2DS2-VASc score was 4 (3, 5). At admission, 16 206 (59.5%) of 27 221 patients with a previous diagnosis of atrial fibrillation were taking OAC agents, and OAC drug use at admission was associated with a lower adjusted odds of in-hospital ischemic stroke (odds ratio, 0.38; 95% CI, 0.24-0.59; P<0.0001). At discharge, prescription of OAC in eligible patients (no contraindications) was 93.5% (n=25 499 of 27 270). In a sensitivity analysis, when excluding only strict contraindications (4.6%, n=1497 of 32 806), OAC prescription at discharge was 80.3%. OAC prescription at discharge was higher in those aged ≤75 years, men, those with heart failure, those with previous atrial fibrillation ablation, and those with rhythm control ( P<0.0001 for all). OAC use was lowest in Hispanic patients (90.2%, P<0.0001). Prescription of OAC at discharge in eligible patients improved over time from 79.9% to 96.6% ( P<0.0001). CONCLUSIONS: Among hospitals participating in the GWTG-AFIB quality improvement program, OAC prescription at discharge in eligible guideline-indicated patients increased significantly and improved consistently over time. These data confirm that high-level adherence to guideline-recommended stroke prevention is achievable.