The status of 200 patients who are living five or more years after mitral commissurotomy is reviewed. In each the original condition was mitral stenosis uncomplicated by any other significant valvular lesion. The data as to such symptoms as dyspnea and edema show that most of these survivors obtained significant relief, though some obtained no relief and a few experienced aggravation of their symptoms. Sixteen patients suffered from recurrent febrile episodes (postcommissurotomy syndrome) within a year after the surgery, and all of them recovered. Fourteen pregnancies occurred, and 12 ended in normal deliveries. Comparison of the cardiologic findings before and after operation showed that these findings do not always explain the symptomatic relief afforded by the operation. It is concluded that even a modest increase in the size of the mitral orifice often affects the dynamics of the heart sufficiently to improve the subjective status of the patient without necessarily affecting murmurs, cardiac size, or electrocardiographic patterns.