To update the European System for Cardiac Operative Risk Evaluation (EuroSCORE) risk model. A dedicated website collected prospective risk and outcome data on 22 381 consecutive patients undergoing major cardiac surgery in 154 hospitals in 43 countries over a 12-week period (May-July 2010). Completeness and accuracy were validated during data collection using mandatory field entry, error and range checks and after data collection using summary feedback confirmation by responsible officers and multiple logic checks. Information was obtained on existing EuroSCORE risk factors and additional factors proven to influence risk from research conducted since the original model. The primary outcome was mortality at the base hospital. Secondary outcomes were mortality at 30 and 90 days. The data set was divided into a developmental subset for logistic regression modelling and a validation subset for model testing. A logistic risk model (EuroSCORE II) was then constructed and tested. Compared with the original 1995 EuroSCORE database (in brackets), the mean age was up at 64.7 (62.5) with 31% females (28%). More patients had New York Heart Association class IV, extracardiac arteriopathy, renal and pulmonary dysfunction. Overall mortality was 3.9% (4.6%). When applied to the current data, the old risk models overpredicted mortality (actual: 3.9%; additive predicted: 5.8%; logistic predicted: 7.57%). EuroSCORE II was well calibrated on testing in the validation data subset of 5553 patients (actual mortality: 4.18%; predicted: 3.95%). Very good discrimination was maintained with an area under the receiver operating characteristic curve of 0.8095. Cardiac surgical mortality has significantly reduced in the last 15 years despite older and sicker patients. EuroSCORE II is better calibrated than the original model yet preserves powerful discrimination. It is proposed for the future assessment of cardiac surgical risk.