To elucidate the factors which are associated with early and late operative results of atrioventricular septal defects, 102 consecutive patients who underwent reparative operation of atrioventricular septal defects (AVSD) in our institution since 1968 were studied. Our operative technique was basically the same through this period. That is the two patch method in its complete form (the so-called Shirotani's method) and preferential use of cleft closure supplemented with Kay-Reed-Wooler type annuloplasty. Early mortality (< 30 days) rate was 18.6%. More than 80% of the early deaths were not related to atrioventricular valve malfunction. Non-complete closure of the cleft, high preoperative pulmonary vascular resistance, deficient atrioventricular valve, and complete form showed independent correlations with early mortality in multiple logistic regression analysis. For operative survivors, event-free survival curves, for atrioventricular valve related reoperations were drawn for various factors. Two late deaths and 3 late atrioventricular-valve-related reoperations occurred. The event-free actuarial survival for operative survivors at 5, 10, and 20 years were 97.0%, 89.4%, and 89.4%, respectively. The survival analysis revealed that preoperative high pulmonary vascular resistance, preoperative severe atrioventricular regurgitation, and preoperative large cardiothoracic ratio in chest radiogram were related with late event occurrence. Higher early mortality in our series may be attributable to relatively advanced pulmonary vascular occlusive disease rather than post repair atrioventricular valve malfunction. On the other hand, our late results were rather good. We concluded that the Shirotani's method and preferential use of cleft closure supplemented with Kay-Reed-Wooler type annuloplasty was effective for most of atrioventricular valves in atrioventricular septal defects. Early surgical intervention before pulmonary vascular disease progression or atrioventricular valve regurgitation development is also important.