Background: Increment of left atrial (LA) volume is an independent prognosticator in various cardiac diseases. However, the changes of LA volume after successful percutaneous mitral valvuloplasty (PMV) and its impact on clinical outcome have not been fully elucidated. We assessed the impact of LA volume changes on long-term clinical outcome after successful PMV. Methods: A retrospective analysis was performed in 319 patients [256 women, age: 40짹11 years] with mitral stenosis who had undergone successful PMV over a 15 year period. Echocardiogram was obtained before and every one year after PMV. LA volume was measured at end-systole using the prolate ellipsoid model. The patients were categorized according to the LA volume 1 month after PMV (cutoff=50ml). Results: Mean follow-up duration was 8짹6 years (2~20 years). LA volume decreased from 94짹51 to 71짹43 ml (p <0.01) 1 month after PMV. Since then, LA volume progressively increased over time and reached pre-PMV level at 8 years (98짹55 ml) after PMV. The increase of LA volume over time was similarly observed regardless of age and cardiac rhythm. Clinical events such as death, mitral replacement, re-PMV, and stroke occurred in 105/319 (33%) patients. Event-free survival was higher in patients with small LA (18 vs.41%, p=0.01). On multiple regression analysis, LA volume 1 month after PMV emerged as an independent predictor of event-free survival. Conclusion: Progressive increase of LA volume was observed even after successful PMV. Larger post-PMV LA volume was associated with poor prognosis.