Percutaneous balloon mitral valvuloplasty is a new technique used in the treatment of adult patients with mitral stenosis. To evaluate the occurrence and severity of mitral regurgitation after balloon valvuloplasty, 24 patients (20 women and 4 men, mean age 57 years) were studied using two-dimensional and Doppler echocardiography before and less than 24 h after this procedure. Mitral valve area increased after valvuloplasty in all patients, from 0.89 +/- 0.07 to 1.61 +/- 0.09 cm2 (p less than 0.001). Before valvuloplasty, 10 patients had no mitral regurgitation, 4 had 1+, 4 had 2+ and 6 had 3+ mitral regurgitation. After valvuloplasty, new mitral regurgitation occurred in six patients. Regurgitation grade did not change in 13 patients (54%), increased by one grade in 8 patients (33%) and by two grades in 3 patients (13%). Left atrial volume decreased in all except one patient from 100 +/- 12 to 83 +/- 12 cm3 (p less than 0.001). Neither age, sex, cardiac rhythm, initial mitral valve area, increase in mitral valve area, morphologic characteristics of the valvular and subvalvular apparatus, previous mitral commissurotomy nor effective balloon dilating area discriminated between those patients with and without an increase in mitral regurgitation after valvuloplasty. Thus, mitral balloon valvuloplasty is frequently associated with an increase in mitral regurgitation. However, in this series, no patient developed severe mitral regurgitation, and left atrial volume decreased in nearly all patients. An increase in mitral regurgitation could not be predicted from any features of the valve or subvalvular apparatus, clinical characteristics of the patients or technical aspects of the procedure.