Family conflict is a salient risk factor for African American adolescents' mental health problems. No study we are aware of has estimated trajectories of their family conflict and whether groups differ in internalizing and externalizing problems during the transition to young adulthood, a critical antecedent in adult mental health and psychopathology. As hypothesized, latent class growth analysis approximated 4 developmental trajectories of family conflict during high school for 681 African American adolescents (49% boys). Trajectory classes differed in anxiety, depressive symptoms, and violent behavior at age 20, supporting expectations that adolescents demonstrating elevated levels and atypical trajectories of family conflict in high school would report greater mental health problems as young adults. Family conflict jeopardizes African American adolescents' transition to young adulthood by contributing to mental health problems.