The long term outcome of 300 consecutive patients following percutaneous mitral commissurotomy (PMC) with the Inoue balloon was analyzed with regard to the incidence of restenosis. There were 256 females and 44 males (mean age 44.4 +/- 9.9 years, range 18-69 years), 52 had previous surgical commissurotomy, 96 were in atrial fibrillation, and 16 had a history of embolism. PCM was carried out with a success rate of 84% (no significant mitral regurgitation and mitral valve area (MVA) > 1.5 cm2). Two hundred and seventy patients were available for clinical and serial echocardiographic studies at six months, 12 months and once a year thereafter (18 patients operated on for mitral regurgitation less than six months after PMC, three patients lost to follow up, nine patients refused to return). MVA increased with PMC from 1.18 cm2 +/- 0.3 to 2.0 +/- 0.3 cm2 and then decreased to 1.8 +/- 0.3 at a mean follow up of 24.0 +/- 13.5 months (range 6-55). Echocardiographic restenosis (RS) (MVA at follow up < 1.5 cm2 with a 50% loss of the initial gain) was found in 38 patients (14%). Twenty-five (66%) of them remained in NYHA class I or II. Restenosis free survival according to the Kaplan-Mayer curve was 93%, 86%, 77% and 73% at 12,24,36 and 55 months respectively. None of the 24 clinical, hemodynamic, echocardiographic or procedural variables used on the Cox proportional hazard regression analysis identified predictors of restenosis free survival. CONCLUSIONS The overall incidence of echocardiographic restenosis post PMC is low (12.6%) in patients followed for a mean period of two years and often occurs without worsened clinical symptoms. It may be difficult to define clinical, echocardiographic or procedural factors as significant predictors of restenosis free survival.