This longitudinal study examined the relation between family instability and the problem behaviors of children from economically disadvantaged families. Family instability was assessed when the children were ages 5 and 7 and included number of residence changes, changes of intimate caregiver relationships, and recent negative life events. The results showed direct concurrent relations between family instability and preschool children's externalizing behavior in the context of other family process variables, relations between subsequent family instability and 1st-grade children's internalizing behavior (i.e., with preschool behavior ratings controlled), and an effect for persistent instability across grade. Moderator effects were also found for child variables, including gender, temperamental adaptability, and prior externalizing scores.