Fifty-one patients with mitral stenosis were studied by M-mode echocardiograms to verify the possibility of predicting if they will require mitral valve replacement or commissurotomy. Fifteen of 18 patients with heavy calcification and restricted or poor valvular mobility underwent mitral valve replacement. Twelve of 14 patients with normal valve amplitude underwent mitral commissurotomy regardless of the presence of valvular calcification. A newly derived measurement, the MT/ST, which is the ratio between the maximal thickness of the widest echo from the mitral valve and the maximal thickness of the left ventricular margin of the interventricular septum, was used to assess valvular calcification. Values above 1.7 were present only in valves with restricted or poor mobility and indicated mitral valve replacement in 14 of 15 cases. All of the patients undergoing mitral valve replacement who had MT/ST ratios between 1.5 and 1.7 had restricted or poor valvular mobility. Of the patients with MT/ST ratios less than 1.5, ten of 12 with normal valvular amplitude underwent mitral commissurotomy, and four of five with restricted valvular mobility underwent mitral valve replacement. We conclude that echocardiographic assessment of mitral valvular calcification and amplitude is useful in predicting patients who will require mitral valve replacement vs mitral commissurotomy.