This study reports the immediate outcome, in-hospital complications, and long-term clinical follow-up of patients undergoing percutaneous mitral balloon valvotomy. In most series, this procedure is reported to increase mitral valve area from less than 1.0 cm2 to at least 2.0 cm2. The most important predictor of the immediate outcome of percutaneous mitral valvotomy is the echocardiographic score. The best results with percutaneous mitral valvotomy occur in those patients with echocardiographic scores of 8 or less. Mortality and morbidity with percutaneous mitral valvotomy are low and similar to surgical commissurotomy. There is less than 1% mortality, a 0% to 3.1% incidence of thromboembolic episodes and stroke, a 1% to 5.2% incidence of severe mitral regurgitation, a 0.2% to 4.1% incidence of pericardial tamponade, and a 3% to 16% incidence of left-to-right shunt. Survival (83 +/- 6% vs 48 +/- 8%), survival with freedom from mitral valve surgery (58 +/- 5% vs 25 +/- 5%), and event-free survival (51 +/- 6% vs 22 +/- 5%) at 80-month follow-up was greater in patients with echocardiographic scores of 8 or less compared with those with scores greater than 8 (P < 0.0001). Thus, the excellent immediate and long term results of percutaneous mitral valvotomy in patients with echocardiographic scores of 8 or less suggest that this procedure may be the treatment of choice in this group of patients.