Aim — to determine echocardiographic and laboratory predictors of D-dimer elevation in patients with atrial fibrillation and atrial flutter. Material and methods. There were 51 patients with paroxysmal or persistent non-valvular atrial fibrillation (n=35, 69%) or atrial flutter (n=11, 21%). Both types of rhythm disturbances were noted in 5 (10%) patients. All patients underwent echocardiography with assessment of right (RA) ad left atrial (LA) dimensions, left ventricular ejection fraction (LV EF) as potentially risk factors of thromboembolic complications. All patients were divided into 2 groups depending on LA volume in order to calculate correlation between LA dimension and D-dimer level. Group 1 — LA volume less than 65 ml (n=22), group 2 — volume over 65 ml (n=29). Correlation of D-dimer and CHA2DS2—VASc score was also analyzed. Results. There was no significant correlation between LV EF and D-dimer level (r=0.253; p=0.142). The same is true for D-dimer and CA2DS2—VASc score (r=0.127; p=0.373). Significant positive correlation (r=0.803; p=0.001) was noted for LA volume and D-dimer level. Patients with LA enlargement had higher D-dimer level than those with normal LA. Conclusion. LA enlargement in patients with atrial fibrillation is followed by increased level of D-dimer and advanced risk of thromboembolic complications. D-dimer may be used as additional marker of stroke and systemic embolic events considering simplicity of its analysis.