Some reliability and validity indices of peer ratings of internalizing (depression, anxiety) and externalizing (aggression) behaviors were explored for elementary school (n = 142) and inpatient (n = 86) 8- to 12-year-old children. Interrater reliabilities for the peer ratings were very good (all above .94) for both samples on all types of behaviors. Peer ratings corresponded significantly with child self-reports on all three traits in both the elementary school and inpatient samples in both the younger (ages 8 and 9) and older (ages 10, 11, and 12) children and in both girls and boys. Peer ratings of depression and aggression corresponded significantly with teacher ratings of those same traits in both samples; however, on anxiety, peer–teacher correspondence was not significant in both samples. For both older and younger children, as well as boys and girls, same-trait peer–teacher correspondence was significant on both depression and aggression, with correspondence on anxiety significant for boys and older children and nonsignificant for girls and younger children. Inpatient children were rated significantly higher by their peers than elementary school children on all three traits. Both samples of children self-reported significantly more depression and anxiety than their peers reported, and inpatient children self-reported significantly less aggression than their peers reported. The potential utility of peer ratings is discussed.