Childhood family adversity influences behavioral and physiological response processes to acute interpersonal stress. Additionally, conflict behaviors in marriage are primary determinants of stress response and related psychological problems in adulthood. As little research has examined these two important literatures simultaneously, further work is warranted to clarify the role of marital conflict behavior in the relation between childhood family adversity and adult cortisol response to conflict. The current study examined relations between childhood family adversity, observed marital conflict behaviors, and salivary cortisol in response to acute marital conflict among 228 different-sex newlywed couples. We examined intrapersonal “actor” effects as candidate mediators of the relation between childhood adversity and cortisol response; and examined interpersonal “partner” effects as candidate moderators of the relation between childhood family adversity and cortisol response. Path analysis using Actor-Partner Interdependence Modeling demonstrated that wives’ childhood family adversity was negatively associated with wives’ cortisol. Wives’ negative conflict behavior (e.g., hostility and distress maintaining attributions) was negatively associated with wives’ cortisol. In the context of higher levels of wives’ negative conflict behavior, husbands’ experiences of childhood family adversity were positively associated with husbands’ cortisol in response to conflict. Results demonstrate the potential lasting impacts of childhood family adversity on later cortisol response to conflict and the important role of wives’ negative conflict behaviors on both husbands and wives. This study adds to the developmental psychopathology and close relationships literature, and further clarifies how stressful childhood experiences and conflict behaviors in marriage “get under the skin” in the form of physiological stress response to conflict.