The new health care environment has increased the need for accurate information about outcomes after pediatric cardiac surgery to facilitate quality improvement efforts both locally and globally. The Risk Adjustment for Congenital Heart Surgery (RACHS-1) method was created to allow a refined understanding of differences in mortality among patients undergoing congenital heart surgery, as would typically be encountered within a pediatric population. RACHS-1 can be used to evaluate differences in mortality among groups of patients within a single dataset, such as variability among institutions. It can also be used to evaluate the performance of a single institution in comparison to other benchmark data, provided that complete model parameters are known. Underlying assumptions about RACHS-1 risk categories, inclusion and exclusion criteria, and appropriate and inappropriate uses are discussed.