Conflict in specific family systems (e.g., interparental, parent-child) has been implicated in the development of a host of adjustment problems in adolescence, but little is known about the impact of family conflict involving multiple family systems. Furthermore, questions remain about the effects of family conflict on symptoms of specific disorders and adjustment problems and the processes mediating these effects. The present study prospectively examines the impact of family conflict and emotional security about the family system on adolescent symptoms of specific disorders and adjustment problems, including the development of symptoms of anxiety, depression, conduct problems, and peer problems. Security in the family system was examined as a mediator of these relations. Participants included 295 mother-father-adolescent families (149 girls) participating across three annual time points (grades 7-9). Including auto-regressive controls for initial levels of emotional insecurity and multiple adjustment problems (T1), higher-order emotional insecurity about the family system (T2) mediated relations between T1 family conflict and T3 peer problems, anxiety, and depressive symptoms. Further analyses supported specific patterns of emotional security/insecurity (i.e., security, disengagement, preoccupation) as mediators between family conflict and specific domains of adolescent adjustment. Family conflict was thus found to prospectively predict the development of symptoms of multiple specific adjustment problems, including symptoms of depression, anxiety, conduct problems, and peer problems, by elevating in in adolescent’s emotional insecurity about the family system. The clinical implications of these findings are considered.