Percutaneous transvenous mitral commissurotomy (PTMC) using Inoue balloon was performed in 270 patients with rheumatic mitral stenosis. Of these 81 (27%), 48 males and 33 females, had juvenile mitral stenosis (age < 20 years, range 9-20 years mean 14 +/- 5). All patients were symptomatic (New York Heart Association [NYHA] class III in 61 patients and class IV in 20 patients). Following PTMC, the mitral valve area (MVA) increased from 0.8 +/- 0.4 to 2.2 +/- 0.5 cm2 (P < 0.001) and the cardiac index increased from 2.4 +/- 0.8 to 3.0 +/- 0.8 L/min/m2 (P < 0.001). Mean transmitral gradients decreased from 24 +/- 8 to 4 +/- 3 mm Hg (P < 0.001). Three (4%) patients had an increase in mitral regurgitation by 1 grade (grade 2/4); however, none required surgery. Significant left to right atrial shunt (Qp/Qs > 1.3: 1) on oximetry was detected in 8 (10%) patients. Overall results were compared to those with adult subgroup of patients with rheumatic mitral stenosis (n = 189, 100 females and 89 males), who underwent PTMC simultaneously. Their age ranged from 21 to 44 years (mean 32 +/- 11 years). The percentage increase in MVA was higher in juvenile as compared to adult patients (172 +/- 61 vs. 154 +/- 69, respectively, P < 0.01). A larger final MVA was achieved in the juvenile group (2.2 +/- 0.5 vs. 1.9 +/- 0.3 cm2, P < 0.05). However, the incidence of increase in mitral regurgitation by 1 grade was similar in two groups (6% vs. 4%, P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)