A total of 168 consecutive patients with predominant rheumatic mitral stenosis were evaluated by transthoracic (TTE) and transesophageal echocardiography (TEE). Of the 168 patients, 35 had previous embolic events (group I) and 133 had no emboli (group II). A total of 77 (45.8%) patients had atrial fibrillation. The frequency of atrial fibrillation was higher in group I than group II (68.6% vs 39.8%, < 0.001). The incidence of left atrial enlargement was greater in group I (p < 0.001). Mitral valve area was found to be smaller in group I compared to group II (p < 0.001). In group I 83.3% and 29.2% of the patients with atrial fibrillation had left atrial spontaneous echo contrast (SEC) and left atrial thrombus, respectively, and 72.7% of the patients with sinus rhythm had left atrial SEC. In group II 79.2% and 20.8% of the patients with atrial fibrillation had left atrial SEC and left atrial thrombus whereas 28.6% and 2.6% of the patients with sinus rhythm had left atrial SEC and left atrial thrombus, respectively. The incidence of left atrial thrombus was significantly different in those patients with compared to those without embolic events (20% vs 9.7%, p < 0.01). In groups I and II, 28 of 35 (80%) and 64 of 133 (48.1%) patients had left atrial SEC (p < 0.01). Patients with left atrial SEC had a greater left atrial size (p < 0.01) and smaller mitral valve area (p < 0.01). Left atrial size was normal in 2 patients with left atrial SEC and SEC was not found in 55 patients with enlarged left atrium. Multiple logistic regression analysis showed that atrial fibrillation, mitral valve area and left atrial enlargement were independent predictors of the SEC (p < 0.001) and left atrial SEC was the principal determinant of thromboembolism.