Although the interpersonal difficulties associated with borderline personality disorder (BPD) are well established, their manifestations within the context of parent-child relationships remain understudied. The current study investigated the relation of maternal BPD symptoms to nonsupportive emotion socialization (i.e., the extent to which mothers punish or minimize their young children's displays of negative emotions), as well as the mediating role of maternal emotion regulation difficulties in this relation. The authors also investigated the moderating role of maternal BPD symptoms in the relation between infant temperamental anger and fear and punitive/minimizing emotion socialization. Using a sample of 99 mother-infant dyads, the authors found that maternal BPD symptoms were significantly related to punitive/minimizing emotion socialization and that maternal emotion regulation difficulties mediated this relation. Moreover, maternal BPD symptoms strengthened the association between mother-reported infant anger and punitive/minimizing emotion socialization. These results extend the growing literature on the impact of maternal BPD on child development.