Epidemiological studies have reported associations between measures of size and weight at birth and disease risk in later life. Alteration in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis in response to prenatal stress has been proposed as one underlying mechanism. The present study investigated in humans the association of prenatal psychosocial stress exposure with subsequent HPA axis regulation in adult life, with a focus on measures of response to challenge and feedback sensitivity. Healthy young adults whose mothers experienced severe stress during their pregnancy in form of major negative life events (e.g. death of someone close; prenatal stress (PS) group, n=31) and an age-matched comparison group (CG, n=30) underwent the Trier Social Stress Test (TSST) and a 1 microg ACTH(1-24) stimulation test. In addition, a diurnal cortisol profile was assessed. ACTH concentrations following a standardized behavioural challenge paradigm (TSST) were marginally significantly higher in PS subjects than in CG subjects (p=.06). Pre-TSST adrenocortical (cortisol) levels were lower (p=.007), whereas the increase in cortisol in response to the TSST was higher (p=.03) in PS subjects compared to CG subjects. Cortisol concentrations following a pharmacological stimulation test simulating pituitary activity (ACTH(1-24) test) were significantly lower in PS than in CG subjects (p=.006). No differences emerged between the two groups in basal diurnal cortisol levels. This study provides first evidence in humans of an association between prenatal psychosocial stress exposure and subsequent alterations in the regulation of the HPA axis.