Echocardiographic and cardiac catheterization findings were compared in 61 patients with mitral stenosis without other significant lesions in an attempt to determine the clinical usefulness of echocardiography in the assessment of such patients. There was a poor correlation between the E-F slope on the echocardiogram and the calculated mitral valve area (r = 0.51). A review of reported data relating the E-F slope to mitral valve area indicated that echocardiographic assessment of mitral valve area had low sensitivity and specificity. The amplitude of excursion of the anterior leaflet did not differ significantly in patients undergoing valvotomy and those undergoind valve replacement. The data obtained suggest that while the echocardiogram is a reliable method of diagnosing mitral stenosis, the E-F slope is an unreliable index of the severity of the lesion.