['Low weight is an established risk factor for mortality after congenital cardiac surgery. Given the advances in the care of neonates and infants after surgery, we sought to examine the effect of low weight on outcomes in the current era.', 'From 2002 to 2012, 2051 infants aged 90 days or less underwent cardiac surgery including 534 (26.0%) with single-ventricle pathology. Regression models examined the effect of low weight (≤ 2.5 kg; n = 274, 13.4%) on early and late outcomes.', 'Overall, the incidence of prematurity, associated chromosomal/extracardiac abnormalities was higher in infants who weighed 2.5 kg or less than in those who weighed more than 2.5 kg; the incidence of single-ventricle pathology was comparable between the 2 groups. In addition, infants who weighed 2.5 kg or less underwent more palliation and had a higher proportion of STAT (Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery) risk category 4 and 5 procedures. Adjusted regression models showed that low weight (≤ 2.5 kg) did not increase unplanned reoperation (odds ratio [OR], 0.90; 95% confidence interval [CI], 0.48-1.67; P = .73) or extracorporeal membrane oxygenation requirement (OR, 1.23; 95% CI, 0.68-2.22; P = .49), however it was associated with significant increase in hospital mortality (OR, 2.15; 95% CI, 1.33-3.50; P = .002). In addition, there was a significant association between low weight and increased duration of postoperative mechanical ventilation and intensive care unit and hospital stays. Adjusted hazard analysis showed that weight equal to or less than 2.5 kg was associated with diminished late survival (hazard ratio, 1.89; 95% CI, 1.39-2.55; P < .001) and that was evident in all patients subgroups (P < .001 for all).'] Are low-weight infants at increased mortality risk after palliative or corrective cardiac surgery?