The “dual-hormone” hypothesis predicts that testosterone and cortisol will jointly regulate aggressive and socially dominant behavior in children and adults (e.g., Mehta & Josephs, 2010). The present study extends research on the dual-hormone hypothesis by testing the interaction between testosterone, cortisol, and personality disorder (PD) traits in predicting externalizing problems in a community sample of adolescent males and females. Participants were 106 youth from the community, ranging in age from 13–18 (Mage = 16.01 years, SDage = 1.29), and their parents. Parents and youth provided ratings on an omnibus measure of personality pathology and externalizing problems. Youth provided saliva samples via passive drool from which testosterone and cortisol levels were obtained. Robust moderation of the joint effects of testosterone and cortisol on parent-reported externalizing problems was found for both higher-order PD traits associated with externalizing psychopathology (Disagreeableness and Emotional Instability). Higher testosterone was associated with externalizing outcomes, but only when cortisol was low, and only among youth with high levels of Disagreeableness and Emotional Instability. These findings provide the first evidence for the dual-hormone hypothesis in a mixed-sex sample of community adolescents, but importantly offer novel evidence for the importance of personality traits. Examination of the joint regulation of externalizing problems by testosterone and cortisol in the context of adolescent personality may help to clarify inconsistent main effects of testosterone and cortisol on clinical externalizing phenotypes.