Borderline personality disorder (BPD) and antisocial personality disorder (ASPD) are among the most debilitating psychiatric conditions. Behaviors and traits associated with these disorders can have profound influences on those surrounding the affected individual. Accordingly, researchers have begun to examine effects of these symptoms on parent-child relationships. Theoretical and empirical work suggests that one mechanism linking maternal psychopathology to child symptoms is familial transmission of emotion dysregulation. The authors examined children's emotion regulation difficulties as a mediator between maternal BPD/ASPD symptoms and child behavior problems 1 year later. Analyses revealed that a composite of maternal BPD/ASPD symptoms had a direct effect on child internalizing, externalizing, and total symptoms. Associations between maternal BPD/ASPD symptoms and youth problems were partially mediated by child emotion regulation difficulties, even with maternal depression and other relevant covariates included in the models. Thus, maternal BPD/ASPD symptoms and child emotion regulation difficulties represent potential targets for prevention of psychopathology among youth.