Background: Persons with a clinically recognized myocardial infarction are at increased risk for atrial fibrillation. However a large proportion of all myocardial infarctions remain clinically unrecognized. Whether subjects with electrocardiographic signs of an unrecognized myocardial infarction are also at an increased risk of developing atrial fibrillation is unknown. The objective of this study was to investigate whether unrecognized myocardial infarction was associated with an increased risk of atrial fibrillation in a prospective population-based cohort study. Methods: The study is set within the prospective population-based Rotterdam Study. The study population comprised 2505 men and 3670 women without atrial fibrillation at baseline. Participants were classified based on electrocardiography, interview, and clinical data into those with recognized myocardial infarction, those with ECG based unrecognized myocardial infarction and those without myocardial infarction. Atrial fibrillation was ascertained from ECG assessments as well as medical records. Results: During a mean follow-up of 11.7 years (SD 5.0), 329 men and 398 women developed atrial fibrillation. Unrecognized myocardial infarction was associated with a two-fold risk of developing atrial fibrillation in men (HR: 2.21, 95%CI: 1.51 to 3.23) compared to men without a history of myocardial infarction, independent of age, and cardiovascular risk factors. In women, unrecognized myocardial infarction was not associated with atrial fibrillation (HR: 0.92, 95%CI:0.59 to 1.44). Conclusion: The presence of an unrecognized myocardial infarction is associated with a twofold increased risk of atrial fibrillation in men, independent of known cardiovascular risk factors. (c) 2013 Elsevier Ireland Ltd. All rights reserved.