The present investigation sought to examine the unique and interactive effects of child maltreatment and interadult violence on children's developing strategies of emotion regulation and socioemotional adjustment, as well as the mediational role of emotion dysregulation in the link between children's pathogenic relational experiences and behavioral outcomes. Person-oriented emotion regulation patterns (EMRPs) were determined based on children's emotional behavioral and self-reported responses to simulated interadult anger. One hundred thirty-nine 4- to 6-year-olds (88 maltreated, 51 nonmaltreated) and their mothers served as participants. Maltreatment history predicted children's EMRPs, with approximately 80% of the maltreated preschoolers exhibiting dysregulated emotion patterns (i.e., undercontrolled/ambivalent and overcontrolled/unresponsive types) compared with only 37.2% of the nonmaltreated controls. Undercontrolled/ambivalent EMRPs were associated with maternal reports of child behavior problems, and were found to mediate the link between maltreatment and children's anxious/depressed symptoms. The present study's findings increase understanding of process relations in pathogenic relational environments, and provide insight into emotion regulation deficits that may impede the development of psychological well-being in maltreated children with varying histories of interadult violence exposure.