Objectives <p>Quality registries often use risk-adjusted benchmarking of mortality to assess hospital performance. The Netherlands Heart Registration (NHR) uses the EuroSCOREII to adjust for hospital differences. However, EuroSCOREII does not include all risk factors that increase mortality risk. Suboptimal benchmarking may have significant negative consequences for all stakeholders. This study aims to assess risk factors not included in EuroSCOREII and their impact on risk-adjusted benchmarking in the Netherlands.</p> Methods <p>This retrospective nationwide cohort study used data from the NHR. Patients undergoing coronary artery bypass grafting and/or surgical aortic valve replacement were included. Patients with surgical mortality were assessed for any additional risk factor not included in the EuroSCOREII by a cardiothoracic surgeon and marked as additional high-risk or not. Risk-adjusted benchmarking was performed using EuroSCOREII. The influence of additional high-risk on benchmarking was assessed through exclusion of additional high-risk patients and through correction for additional high-risk.</p> Results <p>8,480 patients were included of which 156 died within 30-days, 60 out of 156 (38.5%) patients with surgical mortality were classified as additional high-risk. Most frequently mentioned non-cardiac risk factor was high body mass index, cardiac risk factors were ongoing acute myocardial infarction, porcelain aorta and previous unsuccessful revascularization. Both exclusion and correction for additional high-risk led to altered benchmarking positions of hospitals, both improving and degrading hospital rankings.</p> Conclusion <p>38.5% of patients suffer from risk factors not covered in EuroSCOREII, including cardiac, non-cardiac and life-style factors. Including these factors as additional high-risk in the benchmarking process alters the hospital benchmarking positions, indicating that this process may be improved.</p> Graphical abstract <p></p>