We examined aggressive behavior in 6- to 12-year-old children, including 20 children with attention deficit hyperactivity disorder (ADHD) on stimulant medication, 19 children with ADHD on placebo (n = 19), and 32 controls. Children completed a laboratory provocation task designed to measure hostile, instrumental, reactive, and proactive aggression. Children in the ADHD-placebo group exhibited increased proactive and reactive aggression following high levels of provocation compared to controls. On the last trials, instrumental aggression dissipated for controls and hostile aggression dissipated for children in the ADHD-placebo group. Both instrumental and hostile aggression dissipated for children in the ADHD-medication group. (Contains 3 tables and 2 figures.)