On rare occasions, the left atrium may become extremely large in the mitral valvular disease, showing giant left atrium. The giant left atrium frequently produce compressing effects to the adjacent organs, resulting in the postoperative problems with regard to the hemodynamic and respiratory management. We experienced 13 patients with giant left atrium combined with mitral valvular disease from Oct. 1980 through June 1986. Eleven cases underwent mitral valve replacement with left atrial plication and the other 2 cases were underwent mitral valve replacement without left atrial plication. The follow-up period was 19.3 months in average. There were remarkable postoperative improvements in the chest roentgenogram, echocardiogram, lung function test, NYHA functional class in patients who underwent plication procedure. The postoperative mortality was 9% in plication cases and 50% in non-plication cases.