Valproic acid has been used in the treatment of migraine headache for nearly 20 years. During this period of use several additional delivery modes have been developed to either improve tolerability or patient compliance with the divalproex sodium formulation and the extended-release formulation of divalproex sodium. Additionally, an intravenous formulation has become available which permits rapid achievement of therapeutic levels of the drug. There have been a number of reports on the use of valproic acid in migraine and other headache disorders, suggesting it to be an efficacious treatment. This paper reviews the results of the published reports of valproic acid in migraine and other headache disorders, including open-label studies, comparator trials, and double-blind, placebo-controlled trials. These studies have been conducted with the various formulations of valproic acid that have been on the market. The papers utilized in this study were obtained though Medline searches on valproic acid and divalproex sodium coupled with the various headache disorders. Additionally, the CD-ROM of past issues of Headache and Cephalalgia was reviewed for similar keywords. Lastly, the indices of the journal Headache Quarterly were reviewed for additional articles on valproic acid and divalproex sodium. Valproic acid in its various formulations has been demonstrated to be an efficacious and well-tolerated agent for the preventive treatment of migraine, chronic daily headache, and cluster headache. Additionally, it has been demonstrated to be efficacious and well tolerated in treating acute migraine attacks when given as an intravenous solution.