In this study, we analyzed the long-term surgical outcome of partial atrioventricular septal defects during the past 17 years at Seoul National University Hospital. Material and Method: A retrospective analysis on mortality, survival, and reoperation and their risk factors was done in 93 patients who underwent surgical correction of partial atrioventricular septal defects between April 1986 and December 2002. 32 patients were male and 61 were female with a median age of 68 months (3∼818 months) and a mean follow-up period of 108 months (1∼200 months). Result: There were 4 operative deaths (4.3%) and one mortality during the follow-up period. 3, 5, 10, and 15 year actuarial survival rates were 95.7%, 94.3%, 94,3%, and 94.3%, respectively. After the surgical correction, left atrioventricular valve Incompetence was improved in 61patients (67.7%), remained same as the preoperative status in 14 patients (15.1%), and was aggravated in 12 patients (12.9%). Reoperation was performed in 8 patients (9.0%) after a mean interval of 38.6 months (3∼136 months). Freedom from reoperation rates at 3, 5, 10, and 15 years after surgical correction were 94.0%, 91.4%, 91.4%, and 88,2%, respectively Reasons for reoperation were 7 left atrioventricular valve incompetence, 2 left ventricular outflow tract obstruction, a residual atrial septal defect, a left atrioventricular valve stenosis, and a right ventricular failure. Left ventricular outflow tract obstruction was the only statistically significant factor. In ten patients, significant arrhythmia was developed and three of them were supraventricular arrhythmia. Complete atrioventricular block occurred in 7 patients and permanent pacemakers were implanted in six of them. Conclusion: Surgical corrections of partial atrioventricular septal defects were performed with low operative mortality. Since left atrioventricular valve incompetence was the most common cause of reoperation and left ventricular outflow tract obstruction was the only risk factor for reoperation, a precise estimation of the left atrioventricular valve morphology and the structure of left ventricular outflow tract are needed. Although left ventricular outflow tract obstruction rarely developed, reoperation was frequently required and resection of subaortic tissue could be peformed but the possibility of recurrence was high, so modified Konno operation could be performed with satisfactory results. Complete atrioventricular block developed frequently in early periods, but was overcome with a precise anatomical understanding of conduction system and experience.