© 2015, Springer Science+Business Media New York. Psychiatric inpatient hospitalization is a costly intervention for youth. With rates of hospitalization rising, efforts to refine prevention and intervention are necessary. Aggression often precedes severe internalizing behaviors, and proactive and reactive functions of aggression are differentially associated with internalizing symptomatology. Thus, further understanding of the links between functions of aggression and internalizing symptomatology could aid in the improvement of interventions for hospitalized youth. The current study examined parenting styles, gender, and age as potential moderators of the relations between proactive and reactive aggression and internalizing symptoms. Participants included 392 children, 6–12 years of age admitted consecutively to a psychiatric inpatient unit. Reactive aggression was uniquely associated with anxiety symptoms. However, proactive aggression was associated with internalizing problems only when specific parenting styles and demographic factors were present. Although both proactive and reactive subtypes of aggression were associated with internalizing symptoms, differential associations were evident. Implications of findings are discussed.