We retrospectively analyzed our data of percutaneous transvenous mitral commissurotomy (PTMC) using the Inoue balloon with regard to incidence of mitral regurgitation (MR), its likely causative mechanism, and follow up of patients. PTMC was performed in 3,650 patients during the past decade and was successful in 3,276 (89.8%). Severe MR was seen in 120 patients (3.3%), of whom 66 (1.8%) required urgent mitral valve replacement (MVR); among these latter patients, echocardiography showed leaflet rupture in 48 (72.7%), chordal rupture in 12 (18.2%) and excessive commissural tear in six (9.1%). Fifty-four (1.5%) patients with severe MR after PTMC were followed on medical treatment. Follow up data of this cohort were available in 49 patients (1.3%), of whom 30 (0.8%) required MVR. Moderate MR was seen in 188 cases (5.1%), the predominant causative mechanism being excessive commissural tear in 68 (36.2%). Severity of MR worsened in 30 patients (0.8%), of whom 20 (0.6%) required elective MVR on follow up. The MR decreased in 58 (1.6%) patients, excessive commissural tear being the causative mechanism. Thus, significant MR (moderate or severe) after PTMC was seen in 308 patients (8.4%), of whom 116 (3.2%) required MVR urgently or at follow up. All patients with leaflet rupture during PTMC developed severe MR and required urgent MVR. There was a tendency for the severity of MR to decrease with time in cases where excessive commissural tear was the causative mechanism.