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Background: Many very preterm (i.e., <32 weeks of gestation) newborns fail to mount an adequate adrenocortical response to stress or illness, termed relative adrenal insufficiency. Conversely, later in life these infants show features of increased glucocorticoid bioactivity, such as abdominal adiposity, insulin resistance, raised blood pressure, shorter stature and internalizing problem behavior. Summary: Studies suggested that very preterm newborns have impairments along multiple levels of the hypothalamus-pituitary-adrenal (HPA) axis. Among the impairment were defects in: (1) the pituitary responsiveness to exogenous corticotropin-releasing hormone, (2) 11β-hydroxylase activity, and (3) the interconversion between cortisol and inert cortisone. There is some evidence suggesting that later in life these infants have an increased basal secretion rate of cortisol and adrenal hyperandrogenism. However, the response to acute (psychosocial) stress was blunted rather than enhanced in them. The mechanisms explaining this switch in HPA axis activity are complex and not yet fully understood. Key Messages: Very preterm newborns have several impairments along the HPA axis that could impede an adequate adrenocortical response to stress or illness. Later in life, these infants are predisposed to increased HPA axis activity, which could partially explain their phenotype.