Acute valproic acid intoxication is an increasing problem, accounting for more than 5000 calls to the American Association of Poison Control Centers in 2000. The purpose of this paper is to review the pharmacology and toxicology of valproic acid toxicity. Unlike earlier antiepileptic agents, valproic acid appears to function neither through sodium channel inhibition nor through direct gamma-aminobutyric acid agonism, but through an indirect increase in regional brain gamma-aminobutyric acid levels. Manifestations of acute valproic acid toxicity are myriad, and reflect both exaggerated therapeutic effect and impaired intermediary metabolism. Central nervous system depression is the most common finding noted in overdose, and may progress to coma and respiratory depression. Cerebral edema has also been observed. Although hepatotoxicity is rare in the acute overdose setting, pancreatitis and hyperammonemia have been reported. Metabolic and hematologic derangements have also been described. Management of acute valproic acid ingestion requires supportive care and close attention to the airway. The use of controversial adjunctive therapies, including extracorporeal drug elimination and L-carnitine supplementation, will be discussed.