Patients with mitral stenosis in Western countries are relatively old. It is anticipated that percutaneous transseptal mitral commissurotomy (PTMC) may have more complications and may not be as effective in this group of patient as in younger patients due to more calcification and fibrosis of the mitral valve. We analysed the clinical, hemodynamic, echocardiographic data in 296 consecutive patients divided prospectively into two groups; group 1 consisted of 184 patients > or = 40 years and group 2 of 112 patients < 40 years coming mostly from developing countries. The immediate gain in valve area was 2.18 +/- 0.61 cm2 in group 1 vs. 2.31 +/- 0.65 cm2 in group 2 (P = ns). The incidence of acute regurgitation requiring surgical intervention was similar in both groups. Follow-up data up to 5 years after PTMC was available in 170 patients (92.4%) in group 1 (mean 20 +/- 13 months) and 83 patients (74.1%) in group 2 (mean 29 +/- 17 months). Restenosis by Doppler method (valve area less than 1.5 cm2 with loss of at least 50% initial gain in valve area) was found in 33 patients in group 1 (29.2%) vs. 11 (14.9%) in group 2 (P < 0.05). Events free from death, need for mitral valve replacement or repeat PTMC at 5 year follow-up was 76% in group 1 vs. 87% in group 2 (P < 0.05). We conclude that the immediate effectiveness and acute complications of PTMC in patients 40 years and above are comparable to younger patients. Restenosis is clearly higher and there is a trend towards need for mitral valve replacement in patients 40 years and above at follow-up. However, the continuing benefit for the majority of the patients 40 years and above (76% free from adverse events) would suggest that PTMC is an appropriate treatment modality even in the older patients.