In this study, the authors explored whether attachment insecurity moderates the effects of adverse childhood experiences on stress reactivity in the context of borderline personality disorder (BPD). Participants were 113 women (39 with BPD, 15 with some BPD criteria present, 59 without any BPD symptoms) who participated in the Trier Social Stress Test. Saliva samples were collected before and after the stressor and assayed for salivary alpha-amylase (sAA) and cortisol. Adverse childhood experiences were measured using the Childhood Trauma Questionnaire, and attachment by the Experiences in Close Relationships-Revised questionnaire. Results revealed that attachment avoidance and a combination of more adverse childhood experiences and attachment insecurity resulted in higher sAA levels and differences in reactivity to the stressor. Interactions between attachment anxiety and adverse childhood experiences were related to blunted cortisol reactivity. The results suggest that the influence of adverse childhood experiences on stress regulation in BPD may be moderated by attachment-related regulatory processes.