The objective of this study was to prospectively investigate various clinical and echocardiographic variables to predict the left atrial and left atrial appendage clot and spontaneous echo contrast in patients with severe rheumatic mitral stenosis. We studied 200 consecutive patients (112 males and 88 females; mean age 29.6+/-9.6 years). Left atrial clot and spontaneous echo contrast were present in 26 and 53.5% of cases, respectively. There were no significant differences in the mitral valve area, mean transmitral diastolic gradient and left ventricular ejection fraction between patients with and without clot. Patients with clot were older (34.4+/-11.4 vs. 28.2+/-8.5 years, P<0.001), had longer duration of symptoms (41. 4+/-36.0 vs. 28.8+/-22.9 months, P<0.001), more frequent atrial fibrillation and spontaneous echo contrast (69.2 vs. 16.9%, P<0. 00001 and 76.9 vs. 45.3%, P<0.00001, respectively) and larger left atrial area and diameter (41.0+/-12.7 vs. 29.9+/-7.4 cm(2), P<0.00001 and 53.9+/-8.3 vs. 47.6+/-7.4 mm, P<0.0001, respectively) as compared to patients without clot. Similarly patients with spontaneous echo contrast were older (31+/-10.4 vs. 27.8+/-8.3 years, P<0.01), had more frequent atrial fibrillation (48.6 vs. 9.7%, P<0.0001), left atrial clot (37.4 vs. 12.9%, P<0.0001), larger left atrial area and diameter (37.6+/-11.2 vs. 28.1+/-6.7 cm(2), P<0.00001 and 52.2+/-8.3 vs. 45.9+/-6.5 mm, P<0.00001, respectively) and smaller mitral valve area (0.77+/-0.14 vs. 0.84+/-0.13 cm(2), P<0.01) as compared to patients without spontaneous echo contrast. There were no significant differences in the mean transmitral diastolic gradient and left ventricular ejection fraction. On multiple regression and discriminant function analysis, atrial fibrillation and left atrial area were independent predictors of left atrial clot formation. In a subgroup of patients with sinus rhythm, larger left atrial area and presence of spontaneous echo contrast were significantly associated with the presence of clot in left atrium and appendage. We conclude that in patients with severe mitral stenosis, the presence of atrial fibrillation and in the subgroup of the patients with sinus rhythm the presence of large left atrium (> or =40 cm(2)) and spontaneous echo contrast were associated with higher risk of clot formation in the left atrium and might be benefited by prophylactic anticoagulation.