Problem Statement: Aggression is defined as any kind of behavior intended to hurt others. Aggression generally arises due to the interaction between individual (e.g., social and emotional difficulties, low self-esteem, peer rejection, academic failure) and environmental (e.g., poverty, lack of family supervision, limited social support, conflicts within the family) characteristics. Identifying the factors which cause aggressiveness in adolescents is vital to finding precautions against it. Purpose of Study: The purpose of this study was to examine the effects of peer pressure, automatic thoughts and self-esteem variables on the aggression levels of male and female adolescents. Methods: This is a relational and quantitative research aimed to examine the effects of peer pressure, automatic thoughts and self-esteem variables on the prediction of adolescents’ aggression levels. The study sample consisted of 411 volunteer students who were chosen through random sampling from a total of 720 9th grade students from various high schools in Antalya, Turkey. Participants completed the Aggression Questionnaire, Peer Pressure Scale, Automatic Thoughts Scale and Self-Esteem Scale in their classrooms during counseling sessions. Data were analyzed using hierarchical multiple regression analysis. Findings and Results: In the hierarchical multiple regression analysis for female and male adolescents, it was found that peer pressure and