100 patients with endocardial cushion defect of the partial type underwent surgical correction between the years 1957-1975. The age of patients ranged from 3 to 57 years with a mean of 18 years. In 89 patients there was a mitral insufficiency. The repair of the mitral valve was performed in 78 patients; in 21 was repaired also the tricuspidal valve. The hospital mortality was of 8 patients. The mortality was correlated with the age of the patients, the pulmonary pressure and with the presence of malformations of the tricuspid valve. A major complication was represented by a complete atrioventricular block that occurred in 8 patients, in 5 of these the block disappeared before the dimission from the hospital. 86 patients have been followed for a period variable from 2 to 228 months and an average of 61 months. The late mortality was of 4 patients. Two patients have been reoperated of mitral valve replacement because of residual important mitral insufficiency. The phonocardiographic study, done in 50 patients, showed a presence of a holosystolic murmur in 20. The standard X-ray chest and electrocardiogram iid not show important changes between the pre and post operative examination.