OBJECTIVE With improvements in technology and surgical technique, paediatric cardiologists are challenging surgeons to repair balanced atrioventricular septal defects in smaller patients. Early repair minimizes aggressive medical therapy to prevent heart failure, maintains growth, and limits exposure to elevated pulmonary pressures. We compare the outcomes of repair among different-sized children. METHODS From December 2002 to July 2005, 92 patients underwent repair of an atrioventricular septal defect with common atrioventricular valvar orifice and balanced ventricles. We reviewed operative and postoperative data. We excluded patients weighing more than 10 kilograms, but included those who underwent concomitant closure of a patent oval foramen or atrial septal defect, or ligation of a patent arterial duct. Those requiring other concomitant procedures were excluded from the analysis. RESULTS The median weight at repair was 4.9 kilograms, with a range from 2.93 to 7.9 kilograms, and the median age was 5.1 months, with a range from 0.39 to 9.6 months. Operative data included the time required for cardiopulmonary bypass, aortic cross-clamping, and the overall procedure. These times were not significantly affected by decreasing weight. Postoperative continuous data included duration of ventilation and length of intensive care unit and hospital stay. Stay in intensive care (p = 0.006) and hospital (p = 0.007) both increased significantly with decreasing weight. Postoperative categorical data included presence of residual ventricular septal defects, regurgitation across the left atrioventricular valve, and complications. While there was no difference in residual defects (p = 0.166) or valvar regurgitation (p = 0.729), there was a significantly higher presence of complications with decreasing weight (p = 0.0043). There was no mortality, and no persistent heart block requiring placement of a permanent pacemaker. CONCLUSIONS Our data shows that, with the exception of a slightly longer and more complicated postoperative course, early surgery for symptomatic patients with atrioventricular septal defects and common atrioventricular valvar orifice can be undertaken safely and effectively in smaller children with excellent outcomes.