A Phase III Open-Label, Multi-Center, Long-Term Extension Study of Depakote ER in Subjects Who Either Completed or Prematurely Discontinued Due to Ineffectiveness From Study M02-488.

Inclusion Criteria: * Subject and subject's legal representative have voluntarily signed and dated an IRB-approved informed assent form and an IRB-approved informed consent form, respectively, before any study-specific procedures or tests are performed; * The subject was randomized into Study M02-488 and either completed the study or prematurely discontinued due to ineffectiveness; and * The subject is male or non-pregnant, non-lactating female Exclusion Criteria * Female, of childbearing potential, and not using an effective method of birth control (e.g., total sexual abstinence or contraceptives). * Experienced a serious adverse event in Study M02-488 which the investigator considered "possibly" or "probably related" to study drug; or * In the investigator's opinion, long-term treatment with Depakote ER for migraine prophylaxis is contraindicated. * For any reason, subject is considered by the investigator to be an unsuitable candidate to receive divalproex sodium or to participate in this study.