We report 7 children who received gabapentin (GBP) as adjunctive medic ation and subsequently developed behavioral side effects. These behavioral changes consisted of intensification of baseline behaviors as well as new behavioral problems. Behaviors that parents considered most troublesome were tantrums, aggression directed toward others, hyperactivity, and defiance. All behavioral changes were reversible and were managed by dose reduction or discontinuation of GBP. All children had baseline attention deficit hyperactivity disorder and developmental delays.