Background: Arousal-regulating mechanisms are important in explaining individual differences in antisocial behavior. Methods: Alterations in salivary cortisol concentration and cardiovascular activity were studied in 21 boys with oppositional defiant disorder (ODD) and 31 normal controls (NC) during a 2-hour stressful procedure involving frustration and provocation. Results: Baseline levels of heart rate (HR) were significantly lower in the ODD group, but their HR levels were higher during provocation and frustration. Cortisol levels in the ODD group were overall lower than those of the NC group, and the effect of stress seemed to be minimal and similar for both groups; however, individual differences were large. Since anxiety plays an important mediating role in cortisol response, subjects were divided into one of four groups based on the intensity of their externalizing behavior and anxiousness. Cortisol increase due to stress exposure was strongest in highly externalizing and highly anxious subjects; cortisol decrease was strongest in those subjects who were high in externalizing behavior and low in anxiousness. Conclusions: The results of the study support an important role for hypothalamic-pituitary-adrenal axis sympathetic autonomic functioning in persistent antisocial behavior in young boys.