OBJECTIVES: Our goal was to validate the Swedish Cardiac Surgery Registry by reviewing the reported cardiac operations to assess the completeness and quality of the registered data and the EuroSCORE II variables. METHODS: A total of 5837 cardiac operations were reported to the Swedish Cardiac Surgery Registry in Sweden during 2015. A randomly selected sample of 753 patient records (13%) was scrutinized by 3 surgeons at all 8 units in Sweden performing open cardiac surgery in adults. RESULTS: Coverage was excellent with 99% [95% confidence interval (CI) 98-99%] of the performed procedures found in the registry. Reported waiting times for surgery were correct in 78% (95% CI 76-79%) of the cases. The main procedural code was correctly reported in 96% (95% CI 95-97%) of the cases. The correlation between reported and monitored logistic EuroSCORE II had a coefficient of 0.79 (95% CI 0.76-0.82), and the median difference in EuroSCORE II was 0% (interquartile range -0.4% to 0.4%). The majority of EuroSCORE II variables had good agreement and coherence; however, New York Heart Association functional class, preoperative renal dysfunction, left ventricular ejection fraction, Canadian Cardiovascular Society Class IV angina and poor mobility were less robust Postoperative complications were rare and in general had a high degree of completeness and agreement. CONCLUSIONS: The reliability of the variables in the national Swedish Cardiac Surgery Registry was excellent. Thus, the registry is a valuable source of data for quality studies and research. Some EuroSCORE II variables require improved and stricter definitions to obtain uniform reporting and high validity.