Study Designed to Evaluate the Safety of Prophylactic Depakote ER in the Treatment of Adolescents With Migraine

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; Subject is male, or a non-pregnant, non-lactating female; Subject is between 12 and 17 years of age, inclusive, at the Screening Visit; Subject weighs at least 77 lbs. (i.e., 35 kg); Subject currently has diagnosis of migraine headaches consistent with International Headache Society (IHS) criteria; Subject is judged to be in generally good health based on the results of a medical history, physical examination, 12-lead electrocardiogram (ECG), and laboratory profile; and In the investigator's opinion, the subject will benefit from Depakote ER for migraine prophylaxis. Exclusion Criteria: History of allergic reaction or significant sensitivity to valproate or similar drugs; History of noncompliance with medication or medical instructions; Recent (previous 6 months) history of drug and/or alcohol abuse or has a positive urine drug screen, at the Screening Visit, for drugs of abuse (e.g., amphetamines, barbiturates, benzodiazepines, cocaine, opiates, and phencyclidine [PCP]); Female, of childbearing potential, and not using an effective method of birth control (e.g., total sexual abstinence or contraceptives) as judged by the investigator. Use of the following medication classes or any specific drug listed below: anti-depressants, other antiepileptic drugs (AEDs) aspirin and/or aspirin-containing products chronic use of systemic corticosteroids, clonazepam,diazepam, erythromycin, ethosuximide, pemoline, phenobarbital,rifampin,tolbutamide, zidovudine anticoagulant drug therapy; Any serious medical or psychiatric disorder(s), including epilepsy and obesity, that may confound the interpretation of the results from this study; Central nervous system (CNS) neoplasm, CNS infection, demyelinating disease, degenerative neurological disease, or any progressive CNS disease; History of encephalopathy, hepatitis, pancreatitis, or urea-cycle disorder or any underlying condition/disease, which might interfere with study drug absorption or completion of study drug therapy evaluation throughout the duration of the trial; Screening laboratory results indicate the presence of Hepatitis B surface antigen (HBsAg), or Hepatitis C antibody or known history of any positive test result for HIV; Screening laboratory results indicate: Platelet count =/< 100,000/uL ALT or AST =/> 2 times Upper Limit of Normal (ULN); Receipt of an investigational drug within 30 days prior to study drug administration or scheduled to receive any other investigational drug anytime during the study; Participation in a prior Depakote ER migraine study (M02-488 or M02-554); or if for any reason, subject is considered by the investigator to be an unsuitable candidate to receive Depakote or to participate in this study.