Multi-group confirmatory factor analysis and multi-group structural equation modeling were used to test correlates of overt and relational aggression between young adolescent siblings across four groups (i.e., male/male, male/female, female/male, and female/female sibling pairs), using 433 predominately European American families. Similar patterns of associations were found across groups when distinguished by gender composition. Family environment emerged as an important factor in explaining internalizing problems as well as overt/relational aggression for both younger and older siblings. While perceived maternal psychological control was significantly positively related to overt/relational aggression and internalizing problems for younger siblings, it was significantly positively associated with only relational aggression for older siblings. Findings also provided partial support for the positive linkages between young adolescents' aggression and their own and siblings' internalizing problems above and beyond the aforementioned family and maternal variables. Results of the current study extend the understanding of adolescent aggression to a new relational context, or among siblings, and highlight the role of family factors in promoting or buffering the impact of aggression on internalizing behaviors.