Deviant peer process in adolescent friendships has been previously found to predict escalations in substance use, delinquency, and violence in a sample of high-risk adolescent boys. The current study extends past work on deviant peer process by examining its utility in a sample of male and female same-sex dyads. Participants were 105 (51 male, 54 female) adolescents and their same-sex friends. Results showed a small group of adolescents remained high in their antisociality across time, with more boys than girls falling into this group. Antisocial behaviours were intercorrelated within boys of this group, but within girls, physical fighting did not correlate with other antisocial behaviours. Deviant peer process tended to characterize the discourse of both male and female same-sex antisocial dyads, and tended to predict escalations in antisociality over three waves of data collection. Findings provide additional understanding of the interpersonal processes by which antisocial adolescents interact.