Prosocial behaviors, actions intended to help others, may serve a protective function against association with deviant peers and subsequent delinquent and antisocial behaviors. The present study examined the relations among specific types of prosocial behaviors, deviant peer affiliation, and delinquent and aggressive behaviors. Six hundred and sixty-six adolescents (46% girls; M age = 15.33, SD = .47) from Valencia, Spain completed questionnaires of prosocial behaviors, affiliation with deviant peers, antisocial behaviors, and aggression. Results showed that antisocial behaviors were negatively related only to specific forms of prosocial behaviors. Further analyses showed that deviant peer affiliation mediated the relations between compliant prosocial behavior and delinquency and aggression. Although altruism was not directly related to delinquency and aggression, it was indirectly linked to the behaviors via deviant peer affiliation. Discussion focuses on the relevance of specific forms of prosocial behaviors to antisocial behaviors and the risk of deviant peers for prosocial youth.