This study approaches “peer groups” because it considers them to be one of the strongest correlations for antisocial behavior in adolescence. The main intention was to evaluate, in a sample of 283 adolescent scholars of both genders, the processes or dynamics that contribute to non-conventional behavior inside youth groups. In particular, our first objective was to analyze the incidence that behavioral learning and affective relations in peer groups have on the genesis of youthful deviation. The effects that the family and gender can have on the relation of the adolescent with his/her peer group were also analyzed. The findings obtained strengthen the results of other research, indicating that antisocial friendships and certain aspects of groups (conflict, violence, abuse, lack of support) are associated with antisocial and/or criminal conduct in youth of both genders.