This study investigates the longitudinal relationships among child maltreatment, emotion regulation, peer relations, and psychopathology. Data were collected from 215 maltreated and 206 nonmaltreated children aged 6–12 years from low-income families. Children were evaluated by camp counselors on emotion regulation and internalizing/externalizing symptoms, and peer nominations were used to assess peer acceptance and rejection. Structural equation modeling revealed that experiencing neglect, physical and/or sexual abuse, multiple maltreatment subtypes, and earlier onset were linked to emotion dysregulation. Lower emotion regulation at Time 1 was associated with higher externalizing symptoms at Time 1, which contributed to later peer rejection at Time 2, which in turn was related to higher externalizing symptoms at Time 2. Conversely, higher emotion regulation was predictive of higher peer acceptance over time, which was related to lower internalizing symptoms. The findings emphasize the role of emotion regulation as a risk or protective mechanism in the link between maltreatment and later psychopathology through its influence on peer relations. The study highlights the importance of emotion regulation in mediating the effects of maltreatment on psychopathology, particularly through peer relations. It also shows that maltreatment subtypes, such as neglect, physical abuse, and sexual abuse, are differentially related to emotion regulation and adjustment outcomes. The study suggests that early maltreatment onset and multiple maltreatment subtypes are associated with greater risks for emotion dysregulation and later psychopathology. The findings also indicate that peer acceptance and rejection mediate the relationship between emotion regulation and internalizing/externalizing symptoms. The study underscores the need for interventions that promote adaptive emotion regulation skills in maltreated children to improve peer relations and reduce psychopathology.This study investigates the longitudinal relationships among child maltreatment, emotion regulation, peer relations, and psychopathology. Data were collected from 215 maltreated and 206 nonmaltreated children aged 6–12 years from low-income families. Children were evaluated by camp counselors on emotion regulation and internalizing/externalizing symptoms, and peer nominations were used to assess peer acceptance and rejection. Structural equation modeling revealed that experiencing neglect, physical and/or sexual abuse, multiple maltreatment subtypes, and earlier onset were linked to emotion dysregulation. Lower emotion regulation at Time 1 was associated with higher externalizing symptoms at Time 1, which contributed to later peer rejection at Time 2, which in turn was related to higher externalizing symptoms at Time 2. Conversely, higher emotion regulation was predictive of higher peer acceptance over time, which was related to lower internalizing symptoms. The findings emphasize the role of emotion regulation as a risk or protective mechanism in the link between maltreatment and later psychopathology through its influence on peer relations. The study highlights the importance of emotion regulation in mediating the effects of maltreatment on psychopathology, particularly through peer relations. It also shows that maltreatment subtypes, such as neglect, physical abuse, and sexual abuse, are differentially related to emotion regulation and adjustment outcomes. The study suggests that early maltreatment onset and multiple maltreatment subtypes are associated with greater risks for emotion dysregulation and later psychopathology. The findings also indicate that peer acceptance and rejection mediate the relationship between emotion regulation and internalizing/externalizing symptoms. The study underscores the need for interventions that promote adaptive emotion regulation skills in maltreated children to improve peer relations and reduce psychopathology.