BACKGROUND "Gender" reflects social norms for women and men, whereas "sex" defines biological characteristics. Gender-related characteristics explain some differences in access to care for premature acute coronary syndrome (ACS); whether they are associated with cardiovascular outcomes is unknown. OBJECTIVES This study estimated associations between gender and sex with recurrent ACS and major adverse cardiac events (MACE) (e.g., ACS, cardiac mortality, revascularization) over 12 months in patients with ACS. METHODS We studied 273 women and 636 men age 18 to 55 years from GENESIS-PRAXY (GENdEr and Sex determInantS of cardiovascular disease: from bench to beyond-Premature Acute Coronary SYndrome), a prospective observational cohort study, who were hospitalized for ACS between January 2009 and April 2013. Gender-related characteristics (e.g., social roles) were assessed using a self-administered questionnaire, and a composite measure of gender was derived. Outcomes included recurrent ACS and MACE over 12 months. RESULTS Feminine roles and personality traits were associated with higher rates of recurrent ACS and MACE compared with masculine characteristics. This difference persisted for recurrent ACS, after multivariable adjustment (hazard ratio from score 0 to 100: 4.50; 95% confidence interval: 1.05 to 19.27), and was a nonstatistically significant trend for MACE (hazard ratio: 1.54; 95% confidence interval: 0.90 to 2.66). A possible explanation is increased anxiety, the only condition that was more prevalent in patients with feminine characteristics and that rendered the association between gender and recurrent ACS nonstatistically significant (hazard ratio: 3.56; 95% confidence interval: 0.81 to 15.61). Female sex was not associated with outcomes post-ACS. CONCLUSIONS Younger adults with ACS with feminine gender are at an increased risk of recurrent ACS over 12 months, independent of female sex. (C) 2016 by the American College of Cardiology Foundation.