Inclusion Criteria:

• Outpatients ages 5-17 years (inclusive)
• Patients, who in the investigator's opinion have substantial symptoms of mania, depression, or both within the past 2 weeks such that treatment with a pharmacological agent is warranted
• Currently meets DSM-IV criteria for either cyclothymia, or bipolar disorder not otherwise specified (BP NOS) based on the results of both a semi-structured diagnostic research assessment (K-SADS-PL supplemented with sections from the WASH-U K-SADS) (Geller et al., 2001; Kaufman et al., 1997) and a clinical interview with a child and adolescent psychiatrist.
• Offspring of a parent with a bipolar spectrum disorder (based on the results of either the Mini International Neuropsychiatric Interview (MINI)(Sheehan et al., 1998) or the Family History Method (FH-RDC)(Andreasen et al., 1977)
• Has another first or second degree relative with a mood disorder determined by the results of either the MINI or the FH-RDC
• Has participated in at least 4 sessions of psychotherapy specifically focused on the symptoms/management of pediatric mood disorder and continues to have clinically significant symptomatology

Exclusion Criteria:

• Patients who have a history of intolerance to APZ at doses of 0.1mg/kg/day
• Patients who have experienced a manic episode with documented treatment with APZ monotherapy at a dose of 0.2 mg/kg/day
• Patients with an active neurological/medical disorder for which treatment with APZ would be contraindicated
• Patients with clinical evidence of autistic disorder, Asperger's disorder, Rett's syndrome or other pervasive developmental disorder
• Patients with clinical evidence of mental retardation
• Patients who are known to be allergic or hypersensitive to aripiprazole
• Patients who are unable to swallow pills/capsules
• Patients for whom the need for hospitalization during the course of the study appears likely
• Patients who have started a new psychotherapeutic intervention within less than 4 weeks of randomization
• Patients who have a general medical or neurological condition (including clinically significant abnormalities on screening laboratories) that may be considered to be the etiology of the patient's mood disorder
• Patients who have a general medical or neurological condition for which treatment with an atypical antipsychotic would be contraindicated (e.g. tardive dyskinesia)
• Patients who have a general medical or neurological condition that could interfere with the interpretation of clinical response to APZ treatment
• Patients taking psychotropic agents (other than psychostimulants) within one week of baseline (2 weeks for fluoxetine; 3 days for psychostimulants)
• Patients with a suicide attempt requiring medical/psychiatric care within the past 6 months
• Has met DSM-IV criteria for drug/alcohol abuse or dependence within the past 6 months
• Females who are currently pregnant or lactating
• Sexually active females, who in the investigators' opinion are not using an adequate form of birth control