Ten years have passed since the first successful mitral commissurotomy was performed.¹ During these years countless such operations have been done by surgeons all over the world, and there have been many reports of the early results of this procedure. Long-term follow-up studies are essential in the evaluation of any operative procedure. Studies of this type that have been reported ^2-8 indicate that the condition of between two-thirds and three-fourths of the patients operated on is improved. Now that it is possible to operate successfully on the open heart, it is more important than ever to evaluate the long-term results of a closed technique. The question will inevitably arise as to whether open-heart techniques should be used in the treatment of some or even all patients with mitral stenosis. With this in mind the present study was undertaken. The first 131 patients operated on at the Mayo Clinic, of