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model that adjusted for small denominators. Each procedure was assigned a numeric score (the STS–EACTS Congenital Heart Surgery Mortality Score [2009]) ranging from 0.1 to 5.0 based on the estimated mortality rate. Procedures were also sorted by increasing risk and grouped into 5 categories (the STS–EACTS Congenital Heart Surgery Mortality Categories [2009]) that were chosen to be optimal with respect to minimizing within-cat-egory variation and maximizing between-category variation. Model performance was subsequently assessed in an independent validation sample (n 27,700) and compared with 2 existing methods: Risk Adjustment for Con-genital Heart Surgery (RACHS-1) categories and Aristotle Basis Complexity scores. Results: Estimated mortality rates ranged across procedure types from 0.3 % (atrial septal defect repair with patch) to 29.8 % (truncus plus interrupted aortic arch repair). The proposed STS–EACTS score and STS–EACTS categories demonstrated good discrimination for predicting mortality in the validation sample (C-index 0.784 and 0.773, re-spectively). For procedures with more than 40 occurrences, the Pearson correlation coefficient between a procedure’s STS–EACTS score and its actual mortality rate in the validation sample was 0.80. In the subset of procedures for which RACHS-1 and Aristotle Basic Complexity scores are defined, discrimination was highest for the STS– EACTS score (C-index 0.787), followed by STS–EACTS categories (C-index 0.778), RACHS-1 categories (C-index 0.745), and Aristotle Basic Complexity scores (C-index 0.687). When patient covariates were added to each model, the C-index improved: STS–EACTS score (C-index 0.816), STS–EACTS categories (C-index 0.812), RACHS-1 categories (C-index 0.802), and Aristotle Basic Complexity scores (C-index 0.795). Conclusion: The proposed risk scores and categories have a high degree of discrimination for predicting mortal-ity and represent an improvement over existing consensus-based methods. Risk models incorporating these mea-sures may be used to compare mortality outcomes across institutions with differing case mixes. Earn CME credits a