Purpose of the study was to determine the diagnostic accuracy and predictive value of echocadriograhic parameters (transthoracic and transesophageal), obtained by tissue Doppler (TD) and M-mode, used to assess the risk of thrombus formation in the left atrial appendage (LAA) in patients with non-valvular atrial fibrillation, and to compare them with traditional markers of thrombosis. There were enrolled 121 patients with persistent and permanent forms of non-valvular atrial fibrillation. Transthoracic (TTE) and transesophageal (TEE) echocardiography were performed. Patients were divided into three groups depending on the severity of the phenomenon of spontaneous echocontrast (SEC) or the presence of thrombus in the LAA: group 1 (n=73) – patients with no SEC or SEC 1–2 degree; group 2 (n=28) – SEC 3–4 degree; group 3 (n=20) – patients with thrombus in the LAA. The increased risk of LAA thrombus formation was associated with impaired LAA, left atrium and left ventricle structural and functional state. Structural and functional parameters of LAA, assessed by TEE and TTE, were characterized by high diagnostic accuracy and predictive value to determine the risk of thrombosis.