Metabolic syndrome (MS) and atrial fibrillation (AF) are associated with increased cardiovascular disease morbidity and mortality. This analysis evaluated the association between MS and AF in the REasons for Geographic and Racial Differences in Stroke (REGARDS) study. MS was defined using criteria recommended in the joint interim statement from several international societies. AF was defined by electrocardiogram (ECG) and/or self-report and by ECG alone. In patients with 0, 1, 2, 3, 4, and 5 MS components, prevalences of AF by ECG and/or self-report were 5.5%, 7.7%, 8.2%, 9.2%, 9.6%, and 11.5%, respectively (p for trend <0.001). After multivariable adjustment, each MS component except serum triglycerides was significantly associated with AF. The multivariable-adjusted odds ratio for AF, defined by ECG and/or or self-reported history, comparing those with to those without MS was 1.20 (95% confidence interval 1.10 to 1.29). Results were consistent when AF was defined by ECG alone (odds ratio 1.15, 95% confidence interval 0.92 to 1.39). In conclusion, MS is associated with an increased prevalence of AF. Further studies investigating a potential mechanism for this excess risk are warranted. © 2011 Elsevier Inc. All rights reserved.