© 2016 The Authors. Published on behalf of the American Heart Association, Inc. Background-Black US residents experience higher rates of ischemic stroke than white residents but have lower rates of clinically apparent atrial fibrillation (AF), a strong risk factor for stroke. It is unclear whether black persons truly have less AF or simply more undiagnosed AF. Methods and Results-We obtained administrative claims data from state health agencies regarding all emergency department visits and hospitalizations in California, Florida, and New York. We identified a cohort of patients with pacemakers, the regular interrogation of which reduces the likelihood of undiagnosed AF. We compared rates of documented AF or atrial flutter at follow-up visits using Kaplan-Meier survival statistics and Cox proportional hazards models adjusted for demographic characteristics and vascular risk factors. We identified 10 393 black and 91 380 white patients without documented AF or atrial flutter before or at the index visit for pacemaker implantation. During 3.7 ( 1.8) years of follow-up, black patients had a significantly lower rate of AF (21.4%; 95% CI 19.8-23.2) than white patients (25.5%; 95% CI 24.9-26.0). After adjustment for demographic characteristics and comorbidities, black patients had a lower hazard of AF (hazard ratio 0.91; 95% CI 0.86-0.96), a higher hazard of atrial flutter (hazard ratio 1.29; 95% CI 1.11-1.49), and a lower hazard of the composite of AF or atrial flutter (hazard ratio 0.94; 95% CI 0.88- 99). Conclusions-In a population-based sample of patients with pacemakers, black patients had a lower rate of AF compared with white patients. These findings indicate that the persistent racial disparities in rates of ischemic stroke are likely to be related to factors other than undiagnosed AF. ( J Am Heart Assoc. 2016;5:e002492 doi: 10.1161/JAHA.115.002492).