Empirical work has documented positive relationships between attachment security and greater family cohesion, less family conflict, and fewer child adjustment problems, among other positive outcomes. Compromised attachment security is linked with negative outcomes. Using longitudinal data from 999 mother-adolescents dyads surveyed in Belfast, Northern Ireland, the present study examines links among emotional security in the family, mothers' and adolescents' outgroup attitudes, and adolescent engagement in sectarian antisocial behavior. Hypotheses state that emotional security mediates the relationship between mother and adolescent outgroup attitudes, and adolescent outgroup attitude impacts adolescent engagement in sectarian antisocial behavior. Results indicate mother and adolescent outgroup attitudes are correlated at all time points and that emotional security does not mediate the relationship between mother and adolescent outgroup attitude. Adolescent outgroup attitude at times 2 and 4 had a statistically significant effect on adolescent participation in sectarian antisocial behavior at time 6. Implications and future directions are discussed.