Between June 1986 and June 1989, percutaneous balloon valvuloplasty (PBV), using the transseptal, single-balloon technique, was performed in 50 consecutive patients (38 women and 12 men; mean age 54 +/- 14 years) with mitral stenosis. The procedure was technically successful in 48 patients (in one patient the atrial septum could not be crossed, in the other cardiac tamponade occurred). The mean diastolic gradient was decreased from 12.5 +/- 6.6 to 6.1 +/- 3.1 mmHg, mean pulmonary artery pressure (PAP) reduced from 29 +/- 12 to 22 +/- 6 mmHg, and valve opening area increased from 1.0 +/- 0.25 to 1.6 +/- 0.4 cm2. Redilatation had to be undertaken in four patients because of restenosis. Commissurotomy had to be performed in one patient, valve replacement in nine (restenosis in 4, poor primary results in 3, increase in regurgitation in 2). One patient died of a noncardiac cause. Follow-up observations for an average of 14 (3-36) months indicated in 30 of the remaining 33 patients without additional intervention a stable clinical improvement of at least one class (NYHA classification), as well as stable haemodynamic findings (gradient: 6.0 +/- 2.7 mmHg, valve opening area 1.5 +/- 0.3 cm, PAP 23 +/- 7 mmHg. Thus PBV achieved, at least in the medium term, clinical improvement in about two thirds of patients, and an operation was avoided.