Percutaneous mitral commissurotomy has recently been proposed as an alternative to surgery in mitral stenosis. The clinical and hemodynamic results are equivalent to those of surgical treatment. A new technique proposed by Inoue, using a single rubber balloon, with a low incidence of complications, can be performed in a shorter procedure time than the former double balloon technique. A 36 year-old woman with severe mitral stenosis, NYHA FC III, was treated percutaneously using a single rubber balloon designed by Inoue. Her mitral valve area increased from 0.83 to 1.96 cm2, her mean gradient decreased from 15 to 5.8 mmHg and the cardiac output increased from 4.14 to 5.3 l/min. Total procedure time was 2 h and the radioscopic time was 15 min. The follow-up at the fourth month showed persistence of the mitral valve area (2 cm2 at doppler measurement) and the patient was asymptomatic (NYHA FC I). A description of the technique is presented.