Literature on neuroendocrine-behavior relations suggests that cortisol reactivity to social challenge may be associated with children's internalizing problem behavior. To explore this possibility, and the role of control-related beliefs, we studied 102 7-17-year-old clinic-referred children. Measures of problem behavior, depression and anxiety, and control-related beliefs were collected, and Ss' saliva was sampled before and after a parent-child conflict task. Neuroendocrine activation (i.e., cortisol increase) in response to the interaction task was associated with Ss' (a) social withdrawal, social anxiety, and social problems; (b) socially inhibited behavior during the task; and (c) low levels of perceived social contingency and high levels of external attributions for personal successes and failures. Our findings are among the first to link children's behavioral response to social challenge, neuroendocrine activation, cognitions, and psychopathology.