Other valvular lesions associated with pure MS were studied in 202 consecutive patients whose mean age was 43.4 +/- 12.7 years; 76.7% were females. MS was isolated in 63.4%, associated with aortic regurgitation (AR) in 27.7%, aortic stenosis in 1.0%, tricuspid stenosis (+aortic valve lesion) in 1.0%. In isolated MS, 42.4% were NYHA class III or IV, compared with 49.0% in MS + aortic valve lesion. One hundred and sixty-nine (85.4%) patients were operated on; 23.1% had mitral valve replacement, 76.9% had closed (31.4%) or open (45.6%) mitral commissurotomy; 7.1% had associated aortic valve replacement. There were perioperative complications in 20.4%, and the perioperative death rate was 4.1%. Two patients were reoperated in the postoperative course, and 28 patients after this period. The follow-up was 13.3 +/- 4.5 years. The survival rate was 77.7 +/- 4.6% (SE) for isolated MS, and 71.1 +/- 6.3% for MS associated with an aortic valve lesion (NS). The prognosis of MS is very good: the survival rate at 20 years follow-up is 75%. The association of aortic stenosis or tricuspid stenosis does not appear to alter this survival, but numbers are small. Important aortic regurgitation is a significant predictor of higher mortality in patients with MS.