Background: Metabolic syndrome (MS) has been reported to be associated with an increased risk of atrial fibrillation (AF). The aim of this study was to investigate P-wave dispersion (PWD) in patients with MS. Methods: The study population included 66 patients with MS (21 men, 45 women; mean age, 49.7 ± 9.1 years) and 63 control subjects without MS (26 men, 37 women; mean age, 47.0 ± 10.6 years). The diagnosis of MS was based on the National Cholesterol Education Program Adult Treatment Panel III criteria. A 12-lead electrocardiogram was recorded for each subject. The difference between maximum and minimum P-wave duration was calculated and defined as PWD. An echocardiographic examination was also performed for each subject. Results: Maximum P-wave duration and PWD were found to be significantly higher in patients with MS compared with the control subjects (Maximum P-wave duration: 113.5 ± 9.7 ms vs 101.0 ± 8.1 ms, PWD: 37.8 ± 7.6 vs 23.3 ± 5.9, respectively, P < 0.001 for both). However, there was no statistically significant difference between two groups regarding minimum P-wave duration (75.6 ± 6.9 ms vs 77.6 ± 7.8 ms, respectively, P = 0.18). In addition, PWD was positively correlated with age, body mass index, waist circumference, systolic and diastolic blood pressure, triglyceride level, deceleration time, isovolumetric relaxation time and negatively correlated with high-density lipoprotein cholesterol level and early-to-late diastolic velocity ratio. Conclusion: We have shown that patients with MS have higher PWD, indicating increased risk for AF, compared to the control subjects without MS. © 2009 Wiley Periodicals, Inc.