This study examined whether self-esteem mediated the association between peer relationships and internalizing problems (i.e., depression and social anxiety). A total of 7290 (3756 girls) adolescents (ages 13-18 years) completed self-report measures of peer relationships, including direct and indirect victimization, social isolation, friendship attachment (alienation and trust) and friendship quality (conflict and support), as well as self-esteem, social anxiety and depression. Regression analyses indicated that self-esteem partially mediated the relations between social isolation, friendship attachment (alienation) and both depression and social anxiety, whereas friendship attachment (trust) was a partial mediator for depression only. Overall, linkages between peer relationships and depression were more strongly mediated by self-esteem than those between peer relationships and social anxiety. Theoretical and applied implications of these findings are discussed. (Contains 5 tables.)