Although most adopted children are well adjusted, research has consistently found that adopted adolescents are at an increased risk for externalizing behaviors. The present investigation tested a model whereby parent-adolescent negative emotionality traits, adolescent conflict, and adoption status contribute to adolescent externalizing behaviors. The study included 616 families with at least one parent and two adolescent siblings with a maximum 5-year age difference. The analyses used data from the mothers (M age = 45.56, SD = 4.23), fathers (M age = 48.23, SD = 4.42), and the elder sibling (M age = 16.14, SD = 1.5). Findings support two conflict-mediated family processes that contributed to externalizing behaviors: one initiated by parent-adolescent traits and one by adoption status. Findings also underscore the salience of conflict in families and the significance of aggressive traits and negative emotionality. Contrary to previous research, we found that adoption status did not directly add to our explanation of adolescent externalizing behaviors beyond our proposed process. Instead, adoption status was indirectly associated with externalizing problems through a conflict-mediated relationship. (Contains 3 tables and 2 figures.)