Aggression correlates with relatively greater left than right frontal electroencephalographic activity (inverse of EEG alpha power). The present experiment extends this research by manipulating frontal asymmetry and examining its effect on aggression. Participants were assigned to increase left frontal activation or increase right frontal activation by contracting their contralateral hand. They then received insulting feedback and played a game in which they could aggress toward the person who insulted them. Right-hand contractions caused greater left than right central and frontal activation and aggression as compared to left-hand contractions. Within the right-hand contraction condition, greater relative left frontal activity was associated with greater aggression.