The first aim of the present study was to examine associations between different aspects of adolescent friendship relations (i.e., frequency of contact with friends, trust in friends, and perceived friends' deviance) on one hand, and adolescent problem behavior and self-esteem on the other hand. The second aim was to determine whether the findings hold for adolescents from three different ethnic groups and for boys and girls. A sample of 508 Dutch, Turkish, and Moroccan adolescents living in the Netherlands filled in a battery of questionnaires at school. Having contact with deviant friends was the strongest contributor to both aggressive and delinquent problem behavior. Trust in friends was the strongest contributor to self-esteem. In general, gender differences were more pronounced than differences among the ethnic groups. (Contains 2 figures and 6 tables.)