Objective: Children with ADHD often demonstrate poor emotional self-awareness and higher levels of externalizing behavior problems relative to unaffected children. This study examined the relation of deficient emotional self-awareness to externalizing behavior problems in children with ADHD, and the role of emotional reactivity in this relationship. Method: Fifty-one 8- to 12-year-old children with ADHD and their parents completed measures of the children’s emotional and behavioral functioning, as well as a diagnostic structured interview. Results: Logistic regression suggested that more impaired emotional self-awareness was strongly associated with the diagnosis of a comorbid externalizing disorder. Hierarchical regression analyses strongly supported the relation of poor emotional awareness to reactivity-driven externalizing behavior, but not to proactive externalizing behavior. These effects were evident across reporters. Conclusion: This study suggested that poor emotional self-awareness is significantly linked to externalizing problems in children with ADHD, and that dysregulated emotional reactivity plays an important role in this relationship. (J. of Att. Dis. 2013; XX(X) 1-XX)