This study was undertaken to determine the value of transoesophageal echocardiography in the follow-up of patients with severe mitral stenosis having undergone successful percutaneous mitral commissurotomy as defined as a final valve surface area > 1.5 cm2 without > 2/4 mitral regurgitation (MR). Eighty one patients who had undergone successful procedures were studied by transthoracic (TTE) and transoesophageal echocardiography (TOE) before, immediately after (24 to 48 hours) and at medium term (8 +/- 4 months) after balloon commissurotomy. The three main parameters studied were the degree of MR, presence of inter-atrial shunt and spontaneous left atrial contrast. Immediately after commissurotomy the MR was graded 0/4 in 6 patients (7.5%), 1/4 in 48 patients (59%) and 2/4 in 27 patients (33.5%). The TOE showed small traumatic lesions (localised valve tears, rupture of an accessory chordae tendinae) in 9 cases (11%). At medium term follow-up, the MR was stable in 75 patients (93%), decreased by one grade in 3 patients (3.5%), without the occurrence of severe MR. Interatrial shunts were more frequently observed by TOE than by TTE or oximetry with a prevalence of 57%. They usually disappeared at medium term follow-up. There were 3 factors associated with its persistence: a shunt visible at TTE, immediately after commissurotomy, visualisation of an atrial septal defect and a shunt jet width > or = 5 mm at TOE immediately after commissurotomy. Spontaneous contrast was common before the procedure (65%).(ABSTRACT TRUNCATED AT 250 WORDS)