The main purpose of this study was to analyse prosocial and antisocial be-haviour in adolescent athletes in relation to the type of athletic practice, the mo-tivation for engaging in sport, and sex. Three hundred and seventy-four students (130 girls and 244 boys) (age range = 13-18 years) were divided into five groups. The Interpersonal Reactivity Index, the Antisocial Behaviour Questionnaire and the Exercise Behaviour Regulation Questionnaire (BREQ-3) was employed. In the athletes group, girls displayed higher values than boys in perspective-taking (p=.021), fantasy (p=.006), anxiety (p<.001), intrinsic regulation (p=.012), how-ever, showed lower values in external regulation (p=.036). In the nonathletes group, girls showed higher values than boys in perspective-taking (p=.038), per-sonal distress (p=.002), and anxiety (p=.032).Interactions between groups and sex indicated significant differences between boys in fantasy, aggression, isola-tion, and anxiety; there were significant differences in aggression in girls. The girls engaged in more prosocial conduct than the boys, while the nonathlete boys displayed more antisocial behaviour than the athlete boys. In conclusion, the associations between sports practice and the degree of antisocial or proso-cial behaviour in adolescents could not be established. Moreover, several of the motivational factors that were investigated had no clear impact on either type of behaviour.