To assess the feasibility of percutaneous mitral commissurotomy, we undertook dilatation of mitral stenosis in 26 adults. The procedure was unsuccessful in six patients (hemopericardium in one, and five failures). In 20 patients (mean age: 41 +/- 13 years) the procedure was successful. We used a single balloon (Trefoil 3 X 12 mm) in eight patients and two balloons in 12 (Trefoil 3 X 10 mm + 19 mm). After valvuloplasty, valve function was improved: the mean transvalvular gradient decreased from 14 +/- 4 mm Hg to 7 +/- 2 mm Hg (P less than 0.001) and valve area increased from 1.1 +/- 0.2 cm2 to 2.2 +/- 0.4 cm2 (P less than 0.01). In a patient with severe valvular and subvalvular disease, mitral regurgitation increased from grade I to grade III. From this preliminary series, we conclude firstly that percutaneous valvuloplasty is feasible in adults with mitral stenosis, and secondly, that it results in a significant improvement in valve function with a low incidence of complications.