The authors examined changes over a 1-year period in mothers' attributions for child behavior and child oppositional behavior among 53 mothers and nonproblem sons and 44 mothers and sons with attention-deficit/hyperactivity disorder (ADHD). Boys averaged 8 years of age (SD = 11 months) at Time 1. Families were primarily of European Canadian cultural background and most were middle to upper middle class. Initial levels of child oppositionality did not predict changes in mothers' attributions over time. However, initial levels of mothers' attributions of oppositional child behavior to internal, stable, and global causes positively predicted child oppositional behavior, controlling for ADHD versus nonproblem status and the child's initial level of oppositional behavior. Although initial levels of overreactive and nonresponsive parenting also positively predicted child oppositional behavior, the contribution of mothers' attributions remained significant even with parenting variables controlled. Results suggest that mothers' attributions of child oppositional behavior to internal, stable, and global causes may contribute to maintenance of child problems over time and that these parenting cognitions have importance as intervention targets.