ObjectiveTo investigate whether patients’ mortality differs according to the age and sex of surgeons.DesignObservational study.SettingUS acute care hospitals.Participants100% of Medicare fee-for-service beneficiaries aged 65-99 years who underwent one of 20 major non-elective surgeries between 2011 and 2014.Main outcome measureOperative mortality rate of patients, defined as death during hospital admission or within 30 days of the operative procedure, after adjustment for patients’ and surgeons’ characteristics and indicator variables for hospitals.Results892 187 patients who were treated by 45 826 surgeons were included. Patients’ mortality was lower for older surgeons than for younger surgeons: the adjusted operative mortality rates were 6.6% (95% confidence interval 6.5% to 6.7%), 6.5% (6.4% to 6.6%), 6.4% (6.3% to 6.5%), and 6.3% (6.2% to 6.5%) for surgeons aged under 40 years, 40-49 years, 50-59 years, and 60 years or over, respectively (P for trend=0.001). There was no evidence that adjusted operative mortality differed between patients treated by female versus male surgeons (adjusted mortality 6.3% for female surgeons versus 6.5% for male surgeons; adjusted odds ratio 0.97, 95% confidence interval 0.93 to 1.01). After stratification by sex of surgeon, patients’ mortality declined with age of surgeon for both male and female surgeons (except for female surgeons aged 60 or older); female surgeons in their 50s had the lowest operative mortality.ConclusionUsing national data on Medicare beneficiaries in the US, this study found that patients treated by older surgeons had lower mortality than patients treated by younger surgeons. There was no evidence that operative mortality differed between male and female surgeons.