The study will be a multi-center, parallel, group, placebo control, double-blind, randomized controlled trial of lamictal as add-on maintenance treatment in pediatric outpatients (aged 10 to 17 years) diagnosed with Bipolar I disorder. The study consists of 4 phases: Screen (approximately 2 weeks), Open label phase (up to 18 weeks), Randomized phase (up to 36 weeks) and Taper and follow-up phase (up to 4 weeks).

Inclusion Criteria

1. Subject is male or female between the ages of 10 and 17 years, inclusive.
2. Subject has a diagnosis of bipolar I disorder and is currently experiencing a manic/hypomanic, depressed, or mixed mood episode
3. Subject is currently receiving a stable treatment regimen.
4. Subject is living with his/her custodial parent(s) or legal guardian(s) and has contact with them on a daily basis.

Exclusion Criteria

1. Subject has been diagnosed with a primary Axis I disorder (with the exception of bipolar I disorder, ADHD, anxiety disorders, oppositional defiant disorder, or conduct disorder) or any Axis II disorder.
2. Subject currently has signs or symptoms of psychosis or a history of psychosis within the previous four weeks.
3. Subject has been diagnosed with epilepsy, autism, Asperger's syndrome, or Tourette's syndrome.
4. Subject has experienced a serious rash, such as Stevens-Johnson Syndrome or Toxic Epidermal Necrolysis, or a rash otherwise requiring hospitalization.
5. Subject has experienced a rash related to prior LAMICTAL use, or for whom LAMICTAL treatment was discontinued for clinically significant safety reasons.
6. Subject has received any antidepressant medication, or atomoxetine, during the four weeks prior to the Screen Visit.
7. Subject has initiated psychotherapy within 2 months prior to the Screen Visit, or plans to initiate psychotherapy during the trial.
8. Subject in the 10-12 year old age group has a Body Mass Index (BMI) less than or equal 15 or greater than or equal to 30; a subject in the 13-17 year old age group has a BMI less than or equal to 17 or greater than or equal to 34.
9. Subject tests positive for illicit drug use at the Screen Visit, has a history of alcohol or substance abuse or dependence (other than nicotine dependence) within the past three months, or has a positive blood alcohol level at the Screen Visit.
10. Subject, in the investigator's judgment, poses a current homicidal or serious suicidal risk, has made a suicide attempt within the twelve months preceding the Screen Visit, has ever been homicidal.