Backgrounds: Whether echocardiographic parameters of left atrial (LA) size and function, such as LA volume index (LAVi) or late mitral annular (A���) velocity, are related to the development of nonrheumatic atrial fibrillation (AF) has not been evaluated. So, we investigated whether these parameters could predict the development of nonrheumatic AF in Koreans. Subjects and Methods: A total of 14062 patients (>20 years old) who had a comprehensive transthoracic echocardiographic study (TTE) including tissue Doppler imaging were evaluated during 2004. After excluding patients who had valvular heart disease, history of previous AF, pacemaker implantation or cardiac transplantation, 2787 patients who underwent follow-up ECG evaluations with an interval of more than 6 months were analyzed for the development of AF. Results: Newly-developed AF was noted in 42 (1.5%) patients with mean follow-up duration of 31.8짹3.9 months. Average age of patients who developed AF was older than those who did not (63짹13 vs 58짹13 years old, p<0.001). In patients with newly-developed AF, LAVi and relative wall thickness were significantly increased (35.8짹14.3 ml/m² vs. 28.1짹9.6 ml/m², p<0.001 and 0.38짹0.07 vs. 0.36짹0.07, p=0.035, respectively) and A��� velocity was significantly decreased (8.4짹2.0 vs 9.4짹2.4 cm/sec, p=0.012). Area under the receiver-operator characteristics curve to predict AF was 0.68 for the LAVi (p<0.001) with the cutoff value of 28.3ml/m². Cox regression analysis revealed that LAVi >28.3 ml/m² (HR=2.80; 95%CI 1.37~5.34, p=0.005), A' velocity (HR=0.79; 95%CI 0.67~0.94, p=0.006) and age (HR=1.03; 95%CI 1.01~1.07, p=0.010) were related to the development of AF. Conclusions: In addition to the well-known risk factors such as age and LAVi, decreased atrial kick might be an important predictor for the development of nonvalvular AF.