Although a wealth of research has examined the effects of parental mood disorders on offspring maladjustment, studies have not identified whether elevated interparental violence (IPV) may be an exacerbating influence in this pathway. This study examined levels of physical IPV perpetration and victimization in mothers with unipolar depression or Bipolar Disorder (BD) and the processes by which maternal physical IPV moderated adolescents' physical aggression in families with maternal mood disorders. Mothers with lifetime mood disorders were predicted to have elevated IPV compared to well mothers, and maternal IPV was expected to moderate the association between lifetime mood disorders and adolescent aggression. Participants included 61 intact families with maternal depression (n = 24), BD (n = 13), or well mothers (n = 24) and two siblings (ages 10 to 18 years). Using the Conflict Tactics Scale, mothers reported on IPV perpetration and victimization, and adolescents reported on physical aggression. Mothers with BD reported significantly higher IPV perpetration, but not victimization, than depressed or well mothers. An interaction between maternal BD and IPV perpetration was a significant predictor of adolescent aggression. Main effects of maternal IPV victimization and interaction effects of maternal depression and either type of IPV on adolescent aggression were not significant. Adolescents of mothers who have BD and perpetrate IPV may be particularly vulnerable to being aggressive. Prevention and policy efforts to deter transmission of aggression in high‐risk families should target families with maternal BD and intervene at the level of conflict resolution within the family. Aggr. Behav. 9999:XX–XX, 2014. © 2014 Wiley Periodicals, Inc.