By transesophageal echocardiography, the prevalence of left atrial/appendage thrombi and spontaneous echo contrast and the size of the left atrial appendage and their association with clinical and echocardiographic characteristicswere evaluated in 409 nonrheumatic atrial fibrillation outpatients (62 ± 12years) without recent ( < 1 year) embolism. Left atrial/appendage thrombi (2.5%) were associated with diabetes (p < 0.05), heart failure (p < 0.05) and low fractional shortening (p < 0.001); spontaneous echo contrast (12%) with advanced age (p < 0.01), constant atrial fibrillation (p < 0.01), hypertension (p < 0.01), heart failure (p < 0.05), valvular abnormalities (p < 0.01) and large left atrial diameter (p < 0.01), and large left atrial appendages with constant atrial fibrillation (p < 0.05), diabetes (p < 0.05) and valvular abnormalities (p < 0.05).