BACKGROUND: Accurate risk-adjustment models are useful for clinical decision making and are important for minimizing any tendency toward risk-averse clinical practice. In cardiac surgery, emergency patients are potentially at greatest risk of inappropriate risk-averse clinical decisions. UK cardiac surgery outcomes are currently risk-adjusted with EuroSCORE models. The objective of this study was to assess the performance of the EuroSCORE models in emergency cardiac surgery. METHODS AND RESULTS: The National Institute for Cardiovascular Outcomes Research database was used to identify adult cardiac surgery procedures performed in the United Kingdom between April 2008 and March 2011. A subset of procedures (July 2010-March 2011) was used for EuroSCORE II validation. The outcome measure was in-hospital mortality. Model calibration (Hosmer-Lemeshow test, calibration plots, calculation of calibration intercept and slope) and discrimination (area under receiver-operating characteristic curve [area under the curve]) were assessed. In total, 109 988 cardiac procedures at 41 hospitals were included, of which 3342 were defined as emergency procedures. Compared with performance in all cardiac surgery and nonemergency cardiac surgery, the logistic EuroSCORE and EuroSCORE II models had poorer discrimination (area under the curve, 0.703 and 0.690, respectively) and poorer calibration for emergency surgery. The EuroSCORE risk factors of female sex, chronic pulmonary disease, neurological disease, active endocarditis, unstable angina, recent myocardial infarction, and pulmonary hypertension were not identified as important risk factors for emergency cardiac surgery. CONCLUSIONS: Both EuroSCORE models demonstrated poor calibration and comparatively poor discrimination for emergency cardiac surgery. This has important implications when these models are used for clinical decision making or to adjust governance analyses.