Peers contribute to the development of body dissatisfaction and disordered eating behaviors, conditions that show their peak occurrence during the adolescence; however, literature has suggested that peers may influence since earlier ages. Therefore, the objective of this study was to evaluate peer influence, internalization of the body ideal, body dissatisfaction and disordered eating behaviors, in preadolescents vs. adolescents; and to analyze the peer influence in the development of disordered eating behaviors and body dissatisfaction. A total of 273 preadolescents and 175 adolescents' men and women answered four questionnaires, additionally weight and height was measured. The t Student test showed differences between groups only in body mass index, interaction with peers, internalization of body ideal and eating behaviors, being adolescents who obtained higher scores in the first three variables. Path analysis showed that in both groups peers influenced body dissatisfaction, which act as a mediator of disordered eating behavior. It is concluded that body dissatisfaction is not different between preadolescents and adolescents and in both groups peer influence was an important predictive factor.