INTRODUCTION: While specific factors have been associated with outcomes after in-hospital cardiac arrest, the association between sex and outcomes remains debated. Moreover, age-specific sex differences in outcomes have not been fully characterized in this population. METHODS: Adult patients (≥18 years) with an index in-hospital cardiac arrest were included from the Danish In-Hospital Cardiac Arrest Registry (DANARREST) from January 1st, 2017 to December 31st, 2018. Population-based registries were used to obtain data on patient characteristics, cardiac arrest characteristics, and outcomes. Unadjusted and adjusted estimates for return of spontaneous circulation (ROSC), survival to 30 days, survival to one year, duration of resuscitation, and post-cardiac arrest time-to-death were computed. RESULTS: A total of 3266 patients were included, of which 2041 (62%) patients were male with a median age of 73 years (quartiles: 64, 80). Among 1225 (38%) female patients, the median age was 76 years (quartiles: 67, 83). Younger age was associated with higher odds of ROSC and survival. Sex was not associated with ROSC and survival in the unadjusted analyses. In the adjusted analyses, women had 1.32 (95%CI: 1.12, 1.54) times the odds of survival to 30 days and 1.26 (95%CI: 1.02, 1.57) times the odds of survival to one year compared to men. The overall association between sex and survival did not vary substantially across age categories, although female sex was associated with a higher survival within certain age categories. Among patients who did not achieve ROSC, female sex was associated with a shorter duration of resuscitation, which was more pronounced in younger age categories. CONCLUSIONS: In this study of patients with in-hospital cardiac arrest, female sex was associated with a shorter duration of resuscitation among patients without ROSC but a higher survival to 30 days and one year. While the overall association between sex and outcomes did not vary substantially across age categories, female sex was associated with a higher survival within certain age categories.