Surgical outcome data on adolescent and adult congenital heart disease (CHD) undergoing cardiac surgery remains scarce in developing economies. The study aims to evaluate the clinical characteristics and postoperative outcomes in this population, with a focus on identifying risk factors to guide quality improvement initiatives. This retrospective cohort study analyzed 569 CHD patients (aged > 12 years) who underwent surgery at a tertiary center (2018-2023). Data included demographics, surgical details, and clinical outcomes. Major adverse events (MAEs) were defined as cardiopulmonary resuscitation, chest reopening for resuscitation, extracorporeal membrane oxygenation, or death. Univariate and multivariate logistic regressions were performed to identify predictors of MAEs. The median age at surgery was 19.7 years; 42.4% underwent redo sternotomy. Complications occurred in 60.1% of patients, with MAEs in 4.9% and mortality in 2.1%. Multivariate analysis identified significant postoperative bleeding (OR 583.62, 95% CI 16.24-20,970.32) as the main predictor of MAEs. Redo sternotomy doubled the risk of a significant postoperative bleeding (15.4% vs. 6.7%, p