© 2014 Elsevier Inc. All rights reserved. Epidemiological data are limited regarding risk factors of atrial fibrillation (AF) in patients with normal-sized left atria (LA). We evaluated whether traditional risk factors of AF differ between patients with normal-sized and dilated LA. This is a cross sectional study of community-dwelling participants of the Atherosclerosis Risk in Communities study. LA volume index was measured by 2-dimensional echocardiography. LA volume index ≥29 mm3/m2 defined dilated LA. Prevalent AF was defined by electrocardiogram and hospital discharge International Classification of Diseases-9 codes. Multivariate adjusted logistic regression analysis was used to examine whether magnitude of association of risk factors with AF differ by LA cavity size. Interaction of risk factors by LA cavity size was evaluated to determine significance of these differential associations. Of 5,496 participants (mean age 75 ± 5 years, women 58%), 1,230 participants (22%) had dilated LA. The prevalence of AF was 11% in patients with normal-sized LA and 15% in patients with dilated LA. Age >75 years (odds ratio [OR] 1.87, 95% confidence interval [CI] 1.49 to 2.35, interaction p = 0.12) and heart failure (OR 5.43, 95% CI 3.77 to 7.87, interaction p = 0.10) were stronger risk factors for AF in normal-sized LA than dilated LA. Female gender (OR 1.67, 95% CI 1.01 to 2.77, interaction p = 0.09), weight (OR 1.32, 95% CI 1.02 to 1.71, interaction p = 0.19), and alcohol use (OR 1.61, 95% CI 1.08 to 2.41, interaction p = 0.004) were stronger risk factors for AF in patients with dilated LA than normal-sized LA. In conclusion, risk factors of AF may differ by left ventricular cavity size.