This article presents long-term effects of a preventive intervention for young children at high risk for antisocial behavior. Ninety-two children (M age = 4 years) were randomly assigned to an 8-month family intervention or no-intervention control condition and assessed 4 times over a 24-month period. Intent-to-treat analyses revealed significant intervention effects on observed child physical aggression, and significant intervention effects found at the end of the program were maintained at follow-up for responsive parenting, harsh parenting and stimulation for learning. Parent ratings of child aggression did not show significant effects of intervention. (Contains 4 tables and 1 footnote.)