BACKGROUND AND OBJECTIVES: Certain types of arrhythmias have gender differences. Women have a higher incidence of drug-induced QT prolongation than in men. However, there are no reports regarding gender-related differences of the P wave signal averaged electrocardiogram (PWSAE), based on the risk of atrial fibrillation (AF). PWSAE has been recognized as a diagnostic tool for identifying the risk of paroxysmal atrial fibrillation (PAF). We therefore investigated the influence of gender in the parameters of PWSAE and in the risk of AF. SUBJECTS AND METHODS: We recorded 100 PWSAEs in apparently healthy Korean subjects (53 men and 47 women), aged 20 to 79 years. RESULTS: The mean age of the male subjects was 38.2 years and the mean age of the female subjects was 43.2 years (p=0.19). The body surface area (BSA) were larger in men (1.83 m2 vs. 1.53 m2, p<0.05). In men, the filtered P wave duration (fPD) was longer than in women (136.8 msec vs. 125.2 msec, p<0.05). The root mean square voltage in the terminal 20 ms of the filtered P wave (RMS20) was 5.9 micron V in women and 4.5 micron V in men (p<0.05). CONCLUSION: Men have a longer fPD and lower RMS20 than women. The BSA showed a positive correlation with fPD and a negative correlation with RMS20. This study suggests that BSA is an important factor for fPD and RMS20. In addition, as men have a larger BSA as compared with women, we suspect that men have a higher risk of AF as compared with women.