The relation of individual differences in internalizing and externalizing behavior in middle childhood and early adolescence to children's concurrent sibling relationships and their mothers' mood, and to their sibling and mother-child relationships in the preschool period was studied. Thirty-nine younger and 39 older siblings observed at home in the preschool period were studied 5 and 7 years later. Differences in adjustment were related to contemporary sibling relationships and maternal mood, and to sibling and mother-child interaction in the preschool period, even when mothers' current mood was taken into account.