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Introduction: Atrial fibrillation (AF) is often newly diagnosed during heart-rhythm monitoring after ischemic stroke. It is unclear whether this represents pre-existing AF that led to stroke, AF that was triggered by stroke, or AF that would also be seen in stroke-free patients with comparable vascular risk factors.Methods: We compared AF incidence after hospitalization for ischemic stroke, hemorrhagic stroke, and non-stroke conditions. We used inpatient and outpatient claims data from 2008-2015 from a nationally representative 5% sample of Medicare beneficiaries. We used validated ICD-9-CM codes for AF and stroke to identify patients hospitalized with a first-recorded ischemic or hemorrhagic stroke and no documented AF, and matched them in a 1:1 ratio by age, sex, race, calendar year, vascular risk factors, and Charlson comorbidities. We then matched these stroke patients in a 1:1 ratio to patients hospitalized for non-stroke diagnoses. We used survival statistics and Cox regression to compare post-discharge AF incidence among the three matched groups.Results: We matched 2,650 patients with ischemic stroke, 2,650 with hemorrhagic stroke, and 5,300 controls. The post-discharge incidence of AF was 3.4% (95% CI, 3.1-3.7%) per year after ischemic stroke, 2.2% (95% CI, 1.9-2.5%) per year after hemorrhagic stroke, and 2.6% (2.4-2.8%) per year after non-stroke hospitalization. Compared to non-stroke controls, hemorrhagic stroke was associated with a similar risk of AF (HR, 0.9; 95% CI, 0.8-1.0; P = 0.13) and ischemic stroke was associated with a higher risk of AF (HR, 1.4; 95% CI, 1.2-1.6). These findings were unchanged in sensitivity analyses censoring at the time of post-discharge heart-rhythm monitoring or limiting the outcome to AF diagnoses made by a cardiologist.Conclusions: AF was diagnosed more often after hospitalization for ischemic stroke than hemorrhagic stroke or non-stroke conditions.