Gender, racial, and ethnic disparities in healthcare can adversely impact patient safety and lead to poor outcomes. This retrospective study examined surgeon-patient sex discordance and perioperative outcomes among adult patients in Ontario, Canada, undergoing common elective or emergent surgical procedures from 2007 to 2019. Among 1.3 million patients, sex discordance between surgeon and patient was associated with a significant increased likelihood of adverse perioperative outcomes, including death. Subgroup analyses indicate that this relationship is driven by worse outcomes among female patients treated by male surgeons.