We examined whether the sex differences in atrial fibrillation (AF) is related to difference in risk factors leading to AF or due to a differential impact of the same risk factors in 11,806 participants (55.2 % women) from the REGARDS study. Incident AF was ascertained by electrocardiograms and medical history at a follow-up examination. Backwards elimination logistic regression was used to identify AF risk factors in men and women, separately. Over a median follow-up of 9.0years, 588 (11.1%) men and 428 (6.6%) women (p value <0.001) developed AF. Men had a higher risk of AF than women (age and race adjusted odds ratio [OR] [95% confidence interval (CI)]: 1.61 [1.26, 1.75]). Age, white race, height, weight, use of blood pressure lowering medications and history of cardiovascular disease were identified by backward elimination as AF risk factors shared by both sexes. On the other hand, diabetes was an AF risk factor in women but not in men. Among the shared risk factors between men and women, only age showed a stronger association in women than in men [Interaction p-value = 0.003]. Adjustment for the shared risk factors eliminated the sex difference in AF risk (OR [95% CI]: 0.90 [0.74, 1.09]), which was more noticeable in those younger than the median age (62 years) compared to those who were older (interaction p value 0.003). In conclusion, women and men share several AF risk factors, and these shared risk factors explain the sex differences. However, age association with AF differs by sex, and age modifies the associations between sex and other AF risk factors.