This study investigated the changes in treatment procedures for mitral stenosis (MS) and mitral regurgitation (MR) against the background of a decrease in the incidence of rheumatic valvular disease. The study included 3,955 patients with MS undergoing closed mitral commissurotomy (CMC), open mitral commissurotomy (OMC), mitral valve replacement (MVR), or percutaneous transvenous mitral commissurotomy (PTMC) between 1952 and 1991, and 478 patients with MR undergoing MVR or mitral valvuloplasty in the Heart Institute of Japan, Tokyo Women's Medical College. The number of patients with MS undergoing surgical or catheter interventions has decreased and is now about 80 per year, a half of that experienced in the 1960s. CMC and OMC have been replaced by PTMC since the 1990s. The most popular treatment procedure is now MVR. The number of patients with MR undergoing surgery has increased to about 30 per year. Eighty percent of operations for MR are MVR and the others are mitral valvoplasty. Survey of the etiology of MR shows decreased rheumatic disease and increased degenerative disease. The incidence of MR due to ischemic heart disease and hypertrophic obstructive cardiomyopathy has slightly increased.