Abstract: We propose that sex differences in HPA regulation may emerge during puberty and help to explain sex differences in depression. In this study, we examined sex differences in cortisol responses to CRH challenge across pubertal stages in carefully screened control subjects from the Pittsburgh Psychobiologic Studies. Participants were 7-16 years of age, physically healthy, and had no personal or family history of psychiatric disorder. Physician-rated Tanner staging was conducted, followed by CRH challenge sessions including 30-40 minutes pre-infusion baseline, 1 μg/kg CRH infusion, 90-180 minutes of post-infusion measures, and 9-10 plasma cortisol samples. Girls showed increasing total cortisol responses to CRH across Tanner stages, explained by slower recovery from peak cortisol levels, while boys showed similar total responses across Tanner stages. Results show subtle sex differences in the influence of puberty on HPA regulation at the pituitary level, which may represent one factor underlying the emergence of girls' greater rates of depression during this time.