OBJECTIVES: This study evaluates the effect of sex on mortality risks in medieval Ireland to advance our understanding of the social, biological, and environmental factors that were deleterious to female health and survival in the past. MATERIALS AND METHODS: Data on age-at-death and sex was collected on 335 skeletonized individuals from 10 archaeological sites dating to the early medieval (500-1150 ce) and late medieval (1150-1550 ce) periods in Ireland. Transition analysis (TA2) was used to estimate age-at-death for all individuals with visibly fused pelvic and long bone epiphyses. For all other individuals, age-at-death was estimated using dental development and epiphyseal fusion. Morphological traits of the pelvis and cranium and metric measurements were used to estimate sex. A Gompertz-Makeham hazards model with a proportional hazards specification was used to examine the effect of the sex covariate on mortality risks. RESULTS: The Gompertz-Makeham hazards model failed to reveal an effect of sex on mortality risks in this context. No significant temporal variation in the effect of sex on the model was observed across sites. CONCLUSIONS: The results failed to find an effect of the sex covariate on the mortality profile using hazards analysis. However, the similar mortality profiles observed between medieval Irish males and females could reflect cultural barriers and/or differential environmental exposures that counteracted the innate female survival advantage observed today.