Balloon mitral valvotomy was performed in 48 patients (Group I) with mitral restenosis following prior surgical commissurotomy 3-21 years previously. Their results were compared with those of balloon valvotomy in 302 patients without prior commissurotomy (Group II). The procedure was successful in 91.7% of Group I. The mitral valve area, cardiac output, mitral valve gradient, mean left atrial and pulmonary arterial pressures significantly improved following valvotomy (all P < 0.001) in Group I and similar results were obtained in Group II. A comparison of the absolute and percentage change in the mitral valve area following valvotomy amongst the two groups revealed no significant difference (P = N.S.). The baseline clinical characteristics in both the groups were similar except for a higher echocardiographic score (8.64 +/- 1.5 vs. 7 +/- 1.7; P < 0.005) in Group I. Despite the high echo score, achievement of an 'optimal' result and occurrence of postprocedural mitral regurgitation were similar in both groups. The complications included systemic embolus in one patient and increase in mitral regurgitation to > or = 2+ in 2. There were no deaths. Balloon valvotomy for mitral restenosis following surgical commissurotomy is safe, effective and produces clinical and hemodynamic results comparable to those in unoperated cases.