Shyness has been linked to several distinct behavioral antecedents and biological correlates across development, including early behavioral inhibition and neuroendocrine dysregulation. In the present study, we examined whether self-reported history of childhood behavioral inhibition, concurrent cortisol output, and sex affected shyness levels in adults. Results revealed that a history of childhood social behavioral inhibition predicted higher shyness among female adults with high levels of cortisol output. Among women with low cortisol levels, there was no relation between childhood social behavioral inhibition and shyness levels. These associations were not consistent when examining a history of nonsocial behavioral inhibition, or among adult males. These findings highlight the importance of differentiating social versus nonsocial behavioral inhibition when examining relations between childhood temperament and adult shyness. Further, these findings raise the possibility that neuroendocrine dysregulation may have a unique role in predicting and maintaining social behaviors such as shyness depending on sex and individual differences in temperament. (C) 2017 Elsevier Ltd. All rights reserved.