In this longitudinal study, the link between changing relationships between adolescents and their parents and the mediating role of friendships and support from romantic partners on internalizing and externalizing symptoms were analyzed. Based on data on parent—child relationships obtained in 228 adolescents (ages 14 to 17) and their fathers and mothers, three different developmental trajectories were found which were differently linked with internalizing and externalizing symptomatology at ages 17 and 21. The quality of relationships with friends and romantic partners mediated the links between earlier parent—adolescent relationships and later problem behavior. The impact of close relationships with friends and romantic partners as a mediating process between family development trajectories and adaptation was more prominent for females than for males, highlighting the darker side of females' close relationships.