Childhood aggression is often associated with significant psychosocial maladjustment; however, adjustment difficulties may vary based on the function of aggression. The present study used the Behavior Rating Inventory of Executive Function (BRIEF; Gioia et al. Child Neuropsychology 6:235–238, 2000) to examine whether difficulties in particular domains of self-regulation serve as common mechanisms in the association between reactive (versus proactive) aggression and internalizing or externalizing adjustment problems in clinic-referred children. Reactive aggression was associated with poorer behavioral regulation and metacognition, whereas proactive aggression was not associated with poorer self-regulation. Further, the association between reactive aggression and adjustment problems, both internalizing and externalizing, was accounted for by poorer behavioral regulation and metacognitive skills. Gender, age, ADHD diagnosis, IQ, and psychotropic medication status did not account for the results. These findings suggest that self-regulation skills influence adjustment problems in reactively aggressive youth and may be important targets of intervention for such children.