The present study examined the association between peer relationships and externalizing behavior in a sample of high-risk youth during the transition to adolescence. The present sample included youth and their caregivers who participated in a multisite prospective study of youth at risk for maltreatment. Data regarding peer relationships and externalizing behavior were assessed at ages 12, 14, and 16. Maltreatment data were abstracted and coded from official records. A cross-lagged panel mediation model evaluated whether or not peer relationships at age 14 mediated the association between child maltreatment (i.e. prior to age 12) and subsequent externalizing behavior at age 16. Although a mediational model was not supported, individual pathways revealed significant relationships between maltreatment, peer relationships, and externalizing behavior during the transition to adolescence. Findings suggest that recent, ongoing maltreatment is a risk factor for later problem behavior, and that youth involved with negative peers are at risk for subsequent victimization. Intervention opportunities and future directions are discussed.