The purpose of this paper is to estimate the level of self-esteem and aggression in Greek adolescents and examine whether the two constructs are related. A further purpose is to explore the role of family structure in adolescents’ self-esteem and engagement in aggression and the impact of gender in aggressive behaviours. For the above scope, literature review is conducted on the topic of aggressiveness in school, as well as on the relation between self-esteem and aggression and regarding the instruments for measuring self-esteem and aggression in students. Empirically, a questionnaire survey takes place, in a sample of 124 high-school students living in Athens, in the capital of Greece. According to the results, Greek adolescents have satisfactory levels of self-esteem and present low levels of aggression. Adolescent boys are found to engage more in physical aggression, while girls are found to be engaged more in verbal aggression. Self-esteem and aggression are significantly and positively correlated. The present paper contributes to the literature of aggression and self-esteem and suggests focusing on adolescents’ selfesteem, as a means of addressing aggression in schools.