Left atrial (LA) size and function change with chronically increased left ventricular (LV) filling pressures. It remains unclear whether these variations in LA parameters can predict new-onset atrial fibrillation (AF) in asymptomatic patients with aortic stenosis (AS).Data were obtained in asymptomatic patients with mild-to-moderate AS (2.5≤ transaortic Doppler velocity ≤4.0m/s), preserved LV ejection fraction (EF), no previous AF, and were enrolled in the Simvastatin and Ezetimibe in Aortic Stenosis study. Peak-aortic velocity, LA max volume & LA min volume were measured by echocardiography. LA conduit (LA con ) volume was defined as LV stroke volume−LA stroke volume. LA function was expressed as LA-EF (LA max −LA min volume/LA max ).In the 1159 patients included, new-onset AF occurred in 71 patients (6.1%) within a mean follow-up of 4.2±0.9years. Mean age was 66±9.7years, aortic valve area index 0.6±0.2cm 2 /m 2 , LV mass 99.2±29.7g/m 2 , LA max volume 34.6±12.0mL/m 2 , LA min volume 17.9±9.3mL/m 2 , LA-EF 50±15% and LA con volume 45±21mL/m 2 . Baseline LA min volume predicted new-onset AF in Cox multivariable analysis (HR:2.3 [95%CI:1.3–4.4], P<0.01), and added prognostic information on AF development beyond conventional risk factors (likelihood ratio, P<0.01). In comparison of c-indexes LA min volume was superior to all other LA measurements. Net reclassification index improved by 15.9% when adding LA min volume to a model with classic risk factors for AF (P=0.01).LA min volume independently predicted new-onset AF in patients with asymptomatic AS and was superior to LA-EF, LA con and LA max volumes and conventional risk factors.