Objectives Humans—and several other apes—exhibit a unique pattern of post‐natal adrenal maturation; however, the causes and consequences of variation in adrenal development are not well understood. In this study, we examine developmental and age‐related maturation of the adrenal gland (measured via dehydroepiandrosterone‐sulfate [DHEA‐S]) for potential life‐history associations with growth and mucosal immunity in a rural population of immune‐challenged Bolivian juveniles and adolescents. METHODS Salivary DHEA‐S, anthropometrics, and salivary mucosal immunity (secretory IgA [sIgA]) were measured in 171 males and females, aged 8‐23. RESULTS Males with greater energy (i.e. fat) stores showed higher DHEA‐S levels. Controlling for age and energetic condition (to control for phenotypic correlation), higher DHEA‐S was associated with higher mucosal immunity (sIgA) among both males and females. Higher DHEA‐S levels were positively associated with growth (i.e. height and strength) in males. CONCLUSIONS In accordance with predictions derived from life‐history theory, males with higher energy stores secrete more adrenal androgens. This suggests that adrenal maturation is costly and subject to constraints; that is, only males with sufficient reserves will invest in accelerated adrenal maturation. Further, DHEA‐S appears to have a measureable influence on immunocompetence in adolescent males and females; therefore, deficits in DHEA‐S may have important consequences for health and maturation during this period. Adrenal maturation is an important, but understudied component of human growth and development.