Assessment of thromboembolic risk is crucial for proper management of atrial fibrillation (AF) patients. Currently used risk score base only on scarce clinical data and do not take into consideration parameters including echocardiographic findings. The aim of this study was to evaluate if left atrium (LA) enlargement is associated with higher thromboembolic risk assessed by CHADS2 and CHA2DS2-VASc scores in a cohort of unselected non-valvular AF patients. Data from 582 AF hospitalizations occurring between November 2012 and January 2014 were analyzed. All patients underwent a standard transthoracic echocardiography and had their thromboembolic risk assessed in both CHADS2 and CHA2DS2-VASc scores. In 494 enrolled patients (48.5 % male; mean age 73.4 ± 11.5 years) AF was classified as paroxysmal in 233 (47.3 %), as persistent in 109 (22.1 %), and as permanent in 151 (30.6 %) patients. LA was enlarged in 426 (86.2 %) patients. Enlargement was classified as mild in 99 (20.0 %) patients, as moderate in 130 (26.3 %) patients, and as severe in 196 (39.7 %) patients. Patients with enlarged LA had higher mean CHADS2 score (2.0 ± 1.5 vs. 2.6 ± 1.3; p = 0.0005) and CHA2DS2-VASc (3.8 ± 2.0 vs. 4.4 ± 1.8; p = 0.02) score than patients with normal LA. The both mean scores rose along with rising LA diameter. LA enlargement is highly prevalent in AF patients. Higher thromboembolic risk assessed by both CHADS2 and CHA2DS2-VASc scores is associated with presence of LA enlargement. Echocardiographically assessed LA size may be an additional parameter useful in thromboembolic risk stratification of AF patients.