<p>Adolescents in residential care often experience mental health challenges resulting from maltreatment. However, peer relationships can buffer the effects of these maltreatment experiences on adolescents’ mental health. Thus, this cross-sectional study aimed to test the moderating role of peer attachment in the relationship between maltreatment and adolescents’ mental health in residential care. A total of 155 adolescents (57.4% female) aged between 12 and 17&#xa0;years (<i>M</i> = 14.89; <i>SD</i> = 1.59) from 20 residential care settings in Portugal participated in the study. A multi-informant approach was adopted, as staff in the residential care facilities reported on maltreatment experiences and adolescents reported on their relationships with peers and mental health. The results revealed statistically significant moderating effects, as the effect of physical and psychological abuse on externalizing symptoms was higher for adolescents who reported lower quality peer attachment, specifically lower levels of trust. These results highlight the importance of a better understanding of peer dynamics and fostering positive relationships to prevent social exclusion and mental health problems.</p>