Adverse childhood experiences (ACE) are associated with greater neuroendocrine responses to social stress in substance users. The neuropeptide oxytocin might attenuate this relationship. Given sex differences in ACE exposure and neuroendocrine stress reactivity, it is unknown whether this association is similar for males and females. Therefore, this secondary analysis evaluated the interactive effect of sex, ACE, and acute oxytocin administration on neuroendocrine stress responses in adult cigarette smokers (N = 144). Participants completed the Adverse Childhood Experiences Questionnaire at screening and were randomized to receive intranasal oxytocin or placebo before undergoing the Trier Social Stress Task (TSST). Cortisol levels were assessed at pre- and post-medication administration and at 20 and 40 min following the TSST. Generalized linear mixed models were developed to predict post-TSST cortisol levels. Predictors included treatment assignment (placebo vs. oxytocin), sex (male vs. female), ACE (0-10 total score), pre-medication cortisol levels, and minutes since medication administration. The hypothesized three-way interaction between sex, oxytocin, and ACE scores was significant. Linear associations between ACE scores and cortisol reactivity indicated higher ACE scores were associated with attenuated cortisol response in females, regardless of treatment condition. For males, higher ACE scores were associated with heightened cortisol response, an effect that was attenuated by oxytocin. Results indicate that the association between ACE and neuroendocrine reactivity to social stress, as well as the attenuating effect of oxytocin, is differentially impacted by sex. Males with greater childhood adversity may be more likely to benefit from oxytocin’s anxiolytic properties.Copyright © 2020. Published by Elsevier Ltd.