Seven patients with congenital mitral stenosis have been investigated with echocardiography using reflected ultrasound. In all cases the mitral stenosis was combined with other cardiovascular malformations. The results are compared with those obtained at clinical investigation, cardiac catheterization, and operation and/or autopsy. It is concluded that the method is of definite value in diagnosing congenital mitral stenosis, even when this is combined with other cardiovascular malformations. The method is also found to be of value in assessing the severity of mitral stenosis.Three patients have been investigated after mitral valvotomy. It is concluded that the findings at echocardiographic examination agree quite well with the clinical findings and with the results of postoperative cardiac catheterization in the evaluation of the result of mitral valvotomy.