This report reviews behavioral adverse events occurring among adults receiving levetiracetam (LEV) or placebo who participated in short-term, placebo-controlled studies in epilepsy (1023), cognitive disorders (719), or anxiety disorders (1510) and epilepsy patients (1393) observed in long-term trials. Behavioral events (affective, psychotic, and suicidal symptoms) were significantly more common among epilepsy patients than cognition or anxiety patients treated with LEV for similar durations (P=0.022). Affective symptoms occurring at 1% or more often in epilepsy placebo-controlled trials included depression (3.8% LEV-2.1% placebo), nervousness (3.8%-1.8%), hostility (2.3%-0.9%), anxiety (1.8%-1.1%), and emotional lability (1.7%-0.2%). Patients with cognitive and anxiety disorders had lower incidences of these symptoms. The incidence of behavioral events in LEV-treated epilepsy patients was lower than rates reported for some other antiepileptic drugs. These data support the hypothesis that some feature related to epilepsy is the cause of many behavioral events rather than the addition of a specific antiepileptic drug.