This longitudinal study examined the links between child aggression and parenting stress over 4 years. Child aggression was hypothesized to contribute to parenting stress, which should increase aggression. Parents and teachers of 239 German children aged between 6 and 15 years completed measures of child aggression at Time 1 and Time 3, complemented by children’s self-reports of aggression at Time 3. Parents rated their child-focused and parent-focused stress at an intermediate measurement Time 2. Child-focused stress mediated the path from Time 1 to Time 3 aggression in boys and girls, whereas parent-focused stress was unrelated to Time 3 aggression. The findings help to understand the continuity of aggressive behavior in childhood and adolescence and highlight the need to intervene early with families susceptible to parenting stress.