BackgroundAtrial fibrillation (AF) is an important cause of cardioembolic stroke, and population aging has increased its prevalence.ObjectiveTo evaluate the incidence of cardioembolic stroke caused by AF in the city of Joinville, Brazil, as well as previous diagnoses and use of medication.MethodsBetween 2017 and 2020 we extracted data from the population-based Joinville Stroke Registry. Demographic characteristics, diagnosis of AF, and patterns of medication use were collected, and the Trial of ORG 10172 in Acute Stroke Treatment (TOAST) system was used to classify the etiology.ResultsThere were 3,303 cases of ischemic stroke, 593 of which were cardioembolic, and 360 had AF. Of the patients with AF, 258 (71.6%) had a previous diagnosis of the disease, and 102 (28.3%) were newly diagnosed after the stroke. Among patients with a previously-diagnosed AF, 170 (47.2%) were using anticoagulants, and 88 (24.4%) were using other medications.ConclusionDuring the analyzed period, ischemic stroke caused by AF was a significant burden on the population of Joinville, and a considerable number of patients had undiagnosed or untreated AF.