This study addressed early calibration of stress systems by testing links between adversity exposure, developmental stability of hypothalamic-pituitary-adrenal (HPA) axis activity, and behavior problems in a sample of adopted children. Families (N = 200) were assessed when the child was 9 mos, 18 mos, 27 mos, 4.5 yrs, and 6 yrs to collect adversity information—parent psychopathology, stress, financial need, and home chaos. Morning and evening cortisol samples at the final 2 assessments indexed child HPA activity, and parent-reported internalizing and externalizing at the final assessment represented child behavior outcomes. Change in cumulative adversity from 4.5–6 related to higher child morning cortisol, whereas age 6 cumulative adversity related to lower, unstable child evening cortisol. Examination of specific adversity dimensions revealed associations between (1) increasing home chaos and stable morning cortisol, which in turn related to internalizing problems; and (2) high parental stress and psychopathology and lower, unstable evening cortisol, which in turn related to externalizing problems.