46 patients, affected by pure mitral stenosis, underwent echocardiographic study before and after mitral commissurotomy. The following echocardiographic parametres were considered: 1) closing velocity of anterior mitral leaflet (E-F slope); 2) amplitude of the mitral valve motion; 3) intensity and number of echoes coming from the mitral leaflet; 4) posterior leaflet motion; 5) left atrial diameter index; 6) right ventricolar diameter index; 7) left atrial and aorta diameter ratio. Moreover mitral diameter, mitral fibrosis or calcification, and possible mitral incontinence were evaluated intraoperatively before and after commissurotomy. The pre-operative echocardiographic examination of the mitral stenosis showed the following specific aspects: 1) reduced E-F slope, significantly correlated with the severity of the stenosis; 2) abnormally moving posterior mitral leaflet; 3) enlargement of the left atrium, directly correlated with the degree of the mitral stenosis. Correspondence was noted between the echocardiographic and the intraoperative evaluation of the anathomical pattern of mitral valve. Postoperatively the echocardiograms showed: 1) improved E-F slope, directly correlated with the surgical dilatation of the valve; 2) persistent abnormal movement of the posterior mitral leaflet; 3) disappeared correlation between the surgical diameter of mitral valve and the left atrial index. The ECHO proved to be a good diagnostic method for both a qualitative and a semiquantitative evaluation of mitral stenosis. The ECHO is also quite usefull in evaluating modifications induced by commissurotomy.