Many studies have investigated hypothalamus-pituitary-adrenal (HPA) axis responses to psychosocial stress in adults. In children, much less is known about HPA axis reactivity, and a sizable number of studies has not detected a significant cortisol response. Moreover, there is a tack of studies comparing adults' and children's responses to identical stressors. The aim of the present study was to modify an existing laboratory stressor to serve as a potent stressor in children and to allow for direct comparison between children's and adults' stress responses. Thirty children, ages 9-12 (14 female), and 31 young adults, ages 18-25 (17 female), were exposed to the modified protocol (TSST-M). A significant increase in salivary cortisol was observed in response to the TSST-M, F(2.5, 125.4) = 19.65, p <.001, eta(2) = .28, and overall, no differences were found between children's and adults' responses, F(2.5, 125.4) = .31, n.s. Children and adults also showed similar changes in negative and positive affect, both F < 1.18, n.s. and reported a similar amount of distress during the TSST-M, F(1, 57) = .97, n.s. Children did, however, exhibit a significantly greater number of behaviors indicative of distress, F(1, 50) = 6.59, p =.01, eta(2) = .12. This study provides preliminary evidence that the TSST-M is a useful laboratory procedure to induce significant cortisol. responses in children. It also suggests comparable responses in cortisol and self-reported affect in young adults and children. (C) 2009 Elsevier Ltd. All rights reserved.