Objective' To investigate the value of the P-wave area in diagnosing left atrial enlargement in patients with mitral stenosis. Methods' We measured the P-wave area from lead II of a standard 12-lead ECG in 136 consecutive patients with mitral stenosis.We also measured the left atrial diameter with two-dimensional echocardiography. Results' Left atrial enlargement was identified in 120 (88.2%) patients. There was an excellent correlation between P-wave area and left atrial diameter in these patients (r = 0.739, p = 0.001). A P-wave area of '4 msÂ·mv had an 85.8% sensitivity and 93.7% specificity for left atrial enlargement. There was also a smaller but significant correlation between left atrial diameter and the total P-wave duration (r = 0.635, p<0.01) or P-wave amplitude (r = 0.683, p<0.01) in these patients. However, the P-wave area had a better overall sensitivity than the P-wave duration (43.3%) or amplitude (10.8%) in diagnosing left atrial enlargement. Conclusions' Left atrium enlargement can be estimated by P-wave area measured from ECG lead II in patients with mitral stenosis. A P-wave area '4 msÂ·mv serves as a new criterion of left atrial enlargement.