--- - |2+ Background Children adopted from orphanages or other such institutions tend to display blunted reactivity to stressors – even years after arriving in their generally supportive and highly resourced postadoption homes. Puberty, a proposed sensitive period for environmental influences on stress‐mediating systems, may provide an opportunity for postinstitutionalized children to recalibrate stress response systems in accordance with their now more supportive living situations. Methods This cross‐sectional study examined the hypothalamic‐pituitary‐adrenocortical (HPA)‐axis reactivity of 280 children ages 7 through 14 years; 122 children were adopted from institutions in 14 countries between the ages of 6 months and 5 years, after spending an average of 95% of their lives in institutional care, and 158 children of similarly high socioeconomic status in their biological families served as the nonadopted comparison group. All of the children were assessed by nurses for Tanner stage and, on a different day, completed the Trier Social Stress Test for Children. Results Using a linear mixed‐effects model and seven measures of salivary cortisol, results indicated that early‐pubertal postinstitutionalized children showed blunted HPA axis reactivity compared to nonadopted children, but mid/late‐pubertal postinstitutionalized children displayed higher reactivity similar to the nonadopted comparison children. Conclusions This is the first evidence of possible pubertal recalibration of HPA axis reactivity to a psychosocial stressor in postinstitutionalized children, which provides a promising avenue for future research regarding the protective factors of the postadoption environment and subsequent physiological, behavioral, and psychopathological outcomes. - Journal of Child Psychology and Psychiatry, EarlyView.