OBJECTIVES: To explore the relationship between in-hospital mortality following adult cardiac surgery and the time since primary clinical qualification for the responsible consultant cardiac surgeon (a proxy for experience). DESIGN: Retrospective analysis of prospectively collected national registry data over a 10-year period using mixed-effects multiple logistic regression modelling. Surgeon experience was defined as the time between the date of surgery and award of primary clinical qualification. SETTING: UK National Health Service hospitals performing cardiac surgery between January 2003 and December 2012. PARTICIPANTS: All patients undergoing coronary artery bypass grafts and/or valve surgery under the care of a consultant cardiac surgeon. MAIN OUTCOME MEASURES: All-cause in-hospital mortality. RESULTS: A total of 292,973 operations performed by 273 consultant surgeons (with lengths of service from 11.2 to 42.0 years) were included. Crude mortality increased approximately linearly until 33 years service, before decreasing. After adjusting for case-mix and year of surgery, there remained a statistically significant (p=0.002) association between length of service and in-hospital mortality (odds ratio 1.013; 95% CI 1.005-1.021 for each year of 'experience'). CONCLUSIONS: Consultant cardiac surgeons take on increasingly complex surgery as they gain experience. With this progression, the incidence of adverse outcomes is expected to increase, as is demonstrated in this study. After adjusting for case-mix using the EuroSCORE, we observed an increased risk of mortality in patients operated on by longer serving surgeons. This finding may reflect under-adjustment for risk, unmeasured confounding or a real association. Further research into outcomes over the time course of surgeon's careers is required.