The current study used reports from 318 early adolescents to examine the associations of peer-reported gender nonconformity with peer- and self-reported overt and relational victimization and aggression, and possible sex differences in these associations. Multiple-group structural equation modeling revealed that higher levels of peer-reported gender nonconformity were associated with higher self- and peer-reports of overt and relational victimization and aggression among males and females. The association between peer-reported gender nonconformity and peer-reported overt aggression was moderated by participant sex, such that the association was stronger for females compared to males. Results suggest that perceived gender nonconformity is associated with problematic peer relations, especially among females, in early adolescence and implications of these associations are discussed.