The association between children's externalizing behavior problems and mothers' overreactive discipline was examined in a longitudinally assessed sample of toddlers and their mothers. Path analyses indicated that mothers' overreactive discipline and children's externalizing behaviors were significantly and similarly stable over a 2 1/2-year period. No evidence of a cross-time influence of either variable on the other was observed. Mothers' overreactive discipline at Time 2 had a significant effect on Time 2 externalizing behavior. No significant effects of children's behavior on mothers' discipline were found. Mothers' depressive symptomatology and marital discord predicted initial overreactivity and were related to externalizing problems through their relations to overreactivity. The results support the appropriateness of implementing parenting interventions for externalizing problems before age 2 years.