Background: The aim of this study was to investigate longitudinal relations among child maltreatment, emotion regulation, peer acceptance and rejection, and psychopathology. Methods: Data were collected on 215 maltreated and 206 nonmaltreated children (ages 6-12 years) from low-income families. Children were evaluated by camp counselors on emotion regulation and internalizing and externalizing symptomatology and were nominated by peers for peer acceptance and rejection. Results: Structural equation modeling analyses revealed that experiencing neglect, physical and/or sexual abuse, multiple maltreatment subtypes, and earlier onset of maltreatment were related to emotion dysregulation. Lower emotion regulation (Time 1) was associated with higher externalizing symptomatology (Time 1) that contributed to later peer rejection (Time 2), which in turn was related to higher externalizing symptomatology (Time 2). Conversely, higher emotion regulation was predictive of higher peer acceptance over time, which was related to lower internalizing symptomatology controlling for initial levels of symptomatology. Conclusions: The findings emphasize the important role of emotion regulation as a risk or a protective mechanism in the link between earlier child maltreatment and later psychopathology through its influences on peer relations.