The material consists of 250 patients with mitral stenosis who were treated medically in the pre-surgical era and were followed until death or for a minimal period of 10 years; of this group, 115 patients were followed for 20 years. Of the entire series, 61% lived 10 years; in Grade 1, 84% lived 10 years; in Grade 2, 42%; and in Grade 3, 15%. In the 20-year-series, 45% were alive in the 11th year, 30% in the 15th year, and 21% at the end of 20 years. The major symptoms, complications, and causes of death are presented. Survival curves for the surgically treated series of Harken and coworkers are contrasted with those of medically treated cases from the present series and from those of Grant in England and Olesen in Denmark. It is evident from this comparison that the benefit from mitral valvulotomy has been sustained through the ensuing years.