Background: Atrioventricular septal defect (AVSD) is commonly associated with chromosomal abnormalities, especially trisomy 21 or Down syndrome (DS). Surgical repair of complete AVSD (CAVSD) is a complex procedure that carries risks of postoperative morbidity and mortality. Objective: To evaluate the surgical outcomes and to identify the risk factors for hospital mortality and reoperation after repair of CAVSD in DS patients. Patients and Methods: This retrospective cohort study included 65 consecutive DS patients who underwent surgical correction for the complete form of AVSD with or without associated congenital heart diseases during the period from 1^st January 2014 to the end of June 2020. Patients with associated other major cardiac anomalies were excluded. Results: In-hospital mortality was documented in 3 (4.6%) patients, whereas 4 (6.2%) patients needed second unplanned operation for valve/shunt correction. Heart block that needed permanent pacemaker insertion was recorded in 3 (4.6%) patients. In-hospital mortality was significantly associated with prolonged cardiopulmonary bypass (CPB) time (p = 0.008) and the development of renal dysfunction that required dialysis or sepsis (p = 0.004). We found a significant association between the need for second unplanned operation and type A CAVSD (p = 0.041) and the presence of preoperative moderate/severe atrioventricular (AV) valve regurgitation as detected in the transesophageal echocardiography (TEE) (p=0.035). Conclusions: In view of the incidence of the hospital mortality, reoperation, and other postoperative morbidities, we suggest that our outcomes are accepted for surgical repair of CAVSD in DS patients. The CPB time and the development of renal dysfunction that required dialysis and sepsis during the ICU care significantly contributed to the hospital mortality.