BACKGROUND: Female reproductive factors including menopausal age and number of live births have been associated with cardiovascular disease risk, but their role in atrial fibrillation (AF) is underexplored, especially in older adults. METHODS: We analyzed data from the CHS (Cardiovascular Health Study), a US population-based longitudinal study of adults aged ≥65 years including 3065 women reporting their menopausal age and 3236 reporting number of live births at participation. We followed participants for incident AF until June 2015. NT-proBNP (N-terminal pro-B-type natriuretic peptide) was measured at baseline. Maximal P-wave duration, P-wave terminal force in V1, and P-wave dispersion were calculated from baseline ECGs. We assessed the associations of menopausal age, number of live births, and NT-proBNP and electrocardiographic findings with incident AF using linear regression and a Cox model. RESULTS: After a median follow-up of 7.5 years, 1266 women (41.3%) developed AF. Each 5-year increase in menopausal age was associated with lower AF risk (hazard ratio [HR], 0.96 [95% CI, 0.92-1.00]). Menopausal age <40 years was associated with higher AF risk (HR, 1.21 [95% CI, 1.02-1.44]). No association was found between the number of live births and AF risk (HR, 0.98 [95% CI, 0.95-1.02]). Cross-sectional analyses showed younger menopausal age was associated with higher NT-proBNP levels, longer maximal P-wave duration, and longer P-wave dispersion. CONCLUSIONS: Among women aged ≥65 years, earlier menopausal age was associated with higher NT-proBNP, longer P-wave duration, longer P-wave dispersion, and higher AF risk. Number of live births was not associated with these end points.