During the period from january, 1972, to march, 1979, Twenty-four patients underwent mitral valve replacement at the seoul national University Hospital. Their ages ranged from 8 years to 20 years, with 11 patients being 16 years of age or younger at the time of operation. There were 12 males and 12 females and their weight ranged from 25 to 53 Kilograms. Seventeen patients had advanced stages of heart disease as evidenced by the functional classification: 14 cases were in functional class III and 3 cases in functional class IV (New York heart Association). A history suggestive of rheumatic fever was elicited in 75 per cent of our patients. Radiographic evaluation demonstrated marked cardiomegaly in the majority of the patients. The cardiothoracic ratio was over 70 per cent in 5 patients and between 60 and 70 per cent in 17 patients. Cardiac catheterization was carried out in all patients before operation. There were 3 patients with evidence of severe pulmonary hypertension. In 2 patients the pulmonary artery pressures were normal. On physical and hemodynamic examinations, 3 patients had associated with aortic regurgitation, 2 patients had tricuspid regurgitation, 1 patient had tricuspid and aortic regurgitations and 3 patients had atrial septal defect or ventricular septal defect or transposition of great arteries. The pathologic findings of the mitral valve indicated rheumatic valvulitis in 16 patients, while in the remaining 7 the etiology was undetermined. In only one patient the cause was congenital cardiac anomaly. Seventeen patients had predominant mitral regurgitation and 7 patients predominant mitral stenosis. Twenty-nine cardiac prosthetic and bioprosthetic valves were replaced in 24 patients in the past 8 years. This series included 24 mitral, 4 aortic and 1 tricuspid valve replacement. Including in this group were patients who had concomitant aortic valve replacement(3 patients), tricuspid valve replacement(1 patient), tricuspide annuloplasty and closure of ventricular septal defect(1 patient), and closure of atrial septal defect and ventricular septal defec(3 patients). There were five deaths in the postoperative period, resulting in an operative mortality rate of 20.8 per cent. high postoperative mortality was seen in the patients with associated aortic valvular disease and congenital cardiac anomaly.