The links between changes in sibling conflict and intimacy and changes in perceived peer social competence and depression symptoms were examined from middle childhood through adolescence. Participants were mothers, fathers and first- and second-born siblings from 197 White, working/middle class, two-parent families. Peer competence peaked in early adolescence and then declined; depression symptoms were high in middle childhood and, for girls, in middle adolescence. Controlling for parent-offspring relationships and sibling and parent adjustment, increases in sibling conflict were linked to increases in depression symptoms, and increases in sibling intimacy were linked to increases in peer competence and, for girls, decreases in depression symptoms.