OBJECTIVE There are few controlled studies evaluating drug treatment for impulsive aggression. The objective of this study was to evaluate levetiracetam in patients with impulsive aggression, and whether diagnosis or other baseline characteristics predict response. METHOD Outpatients with clinically significant impulsive aggression (meeting Coccaro et al. revised criteria for intermittent explosive disorder), without other psychiatric symptomatology clearly requiring treatment, were randomly assigned to levetiracetam or placebo, double-blind, for 10 weeks, at a variable dose with a maximum dose of 3000 mg/day. The primary efficacy measure was change in the total aggression score from the revised Overt Aggression Scale-Modified. The study was conducted from September 2005 to July 2006. RESULTS Of 40 patients (20 in each treatment group), 34 completed at least 4 weeks of treatment with double-blind medication. There was no overall statistical evidence of levetiracetam benefit, and no subgroup more responsive to levetiracetam could be identified. CONCLUSIONS Levetiracetam was not as efficacious as oxcarbazepine was in a prior similar study. Additional studies of medications for impulsive aggression seem warranted.