BACKGROUND: Patient-surgeon sex concordance influences postoperative outcomes in general surgery, but its relevance in cardiac surgery is unknown. METHODS: This was a cohort study of 223 065 Medicare beneficiaries undergoing coronary artery bypass grafting, surgical aortic valve replacement, and/or proximal aortic surgery from 2010 to 2021, stratified by surgeon and patient sex. The primary and secondary outcomes were composites of mortality and morbidity (myocardial infarction, stroke, and all-cause readmission) at 30 days and 5 years postoperatively, respectively. Multivariable regression analysis identified independent associations. RESULTS: The male surgeon-male patient group comprised 59.9% (133 533/223 065), the female surgeon-male patient group comprised 8.3% (18 623/223 065), the female surgeon-female patient group comprised 3.8% (8466/223 065), and the male surgeon-female patient group comprised 28.0% (62 443/223 065) of the cohort. There was no difference in the incidence of the 30-day composite outcome between groups and no independent association of sex concordance with the 30-day composite outcome (odds ratio sex discordance, 1.00 [95% CI, 0.96-1.04]; P=0.84); the interaction between patient sex and sex discordance was not significant (P=0.75). The incidence of the 5-year composite outcome was higher in the male surgeon-male patient than the female surgeon-male patient group (67.2% [89 795/133 533] versus 65.3% [12 160/18 623]; P<0.0001), and in the male surgeon-female patient than the female surgeon-female patient group (75.7% [47 262/62 443] versus 74.0% [6264/8466]; P=0.0006). There was no association of sex concordance with the 5-year composite outcome (hazard ratio sex discordance, 1.00 [95% CI, 0.98-1.02]; P=0.69); the interaction between patient sex and sex discordance was not significant (P=0.89). CONCLUSIONS: There was no independent association of patient-surgeon sex concordance with 30-day or 5-year outcomes after cardiac surgery.