This study compared the immediate and long-term outcome of percutaneous transvenous mitral commissurotomy (PTMC) in patients who had (restenosis group, n = 9) or had not (de novo group, n = 27) previously undergone surgical mitral commissurotomy. The baseline echocardiographic score, which is an index of deformity of the mitral valve apparatus, was significantly higher in the restenosis group than in the de novo group (11 +/- 3 vs 7 +/- 2, p < 0.01), although age, left atrial diameter, and the prevalence of atrial fibrillation were similar. PTMC was performed by the Inoue technique, and was abandoned in 1 patient from the restenosis group because of failed trans-septal puncture. Including this patient, 3 patients (33%) in the restenosis group had a thickened atrial septum compared with only 1 (4%) in the de novo group. One patient in the de novo group developed cardiac tamponade during this procedure. In both groups, the mitral valve area increased significantly, but the success rate of PTMC was lower in the restenosis group (4/9 patients, 44%) than in the de novo group (22/27 patients, 81%) (p < 0.05). Twenty-six patients who had successful PTMC were followed up over 51 +/- 14 months. After 4 years of follow-up. 3 out of 4 patients (75%) in the restenosis group and 3 out of 22 patients (14%) in the de novo group demonstrated echocardiographic restenosis (p < 0.01). Stepwise multivariate analysis revealed that the echocardiographic score was the only significant predictor of both the immediate and long-term outcome. In conclusion, the immediate and long-term outcome of PTMC were worse in patients who had undergone previous surgical mitral commissurotomy than in those who had not. This was mainly attributable to the difference in the severity of the valvular lesions. In addition, our data suggested that a thickened atrial septum, possibly related to surgery as well as chronic rheumatic disease, may affect the performance of PTMC.