Background: Percutaneous mitral commissurotomy (PMC) has become the reference treatment for mitral stenosis in patients with favorable valvular anatomy. 
Purpose: We sought to evaluate the safety and effectiveness of PMC for patients with mitral stenosis. 
Methods: Late results of PMC were assessed in 1035 consecutive patients at our institution. A good immediate result was defined as valve area ≥ 1.5 cm² without mitral regurgitation > 2/4. PMC are using a double balloon or the Inoue balloon. 
Results: 
The average age in our population was 35 ± 12 years. Good immediate results were obtained in 92.4%. 
The 20-year rate of good functional results (survival without cardiovascular death, mitral surgery, or repeat percutaneous mitral commissurotomy and in New York Heart Association class I or II) was 47.6 ± 2.4%. 
A multivariable Cox model identified 3 predictive factors of poor late functional results: Prior commissurotomy (p=0.014), Wilkins score>8 (p<0.0001) and final mitral valve area <1.8 cm² (p<0.0001). 
The scoring system was derived from the final multivariable model in the derivation cohort of 987 patients, corresponding to predicted good functional results in the validation cohort.
Conclusions: Twenty years after percutaneous mitral commissurotomy in a population of patients with varied characteristics, 47% still had good functional results. Prediction of late functional results is multifactorial and strongly determined Wilkins score and the quality of immediate results. A simple validated scoring system is useful for estimating individual patient outcome.