Interparental conflict is a common source of psychosocial stress in the lives of children. The purpose of this study was to examine the association between recent interparental conflict and one component of the physiological stress response system, the hypothalamic-pituitary-adrenal (HPA)-axis. Parents of 42 children (ages 8–13 years) completed daily diaries of interparental conflict for 8 weeks. At the end of the 8 weeks, youth participated in the Trier Social Stress Test for Children (TSST-C) while providing 2 pre- and 4 poststress salivary cortisol samples. Youth whose fathers reported a pattern of increasing interparental conflict over the past 8 weeks demonstrated an exaggerated HPA-axis response to acute stress. Mother-reported interparental conflict was not associated with children’s HPA-axis responses without accounting for fathers’ reports. When accounting for fathers’ reports, the offspring of mothers reporting higher average daily interparental conflict demonstrated an attenuated HPA-axis response to the stressor. By estimating both average exposure and recent patterns of change in exposure to conflict, we address the circumstances that may prompt attenuation versus sensitization of the HPA-axis in the context of interparental conflict. We conclude that the HPA-axis is sensitive to proximal increases in interparental conflict which may be one pathway through which stress affects health across development, and that incorporating father’s reports is important to understanding the role of the family environment in stress responses. This study further demonstrates the value of using intensive repeated measures and multiple reporters to characterize children’s psychosocial environment.