This article reviews juvenile onset bipolar disorder with regard to history, diagnosis, comorbidity, differential diagnosis, prevalence, etiology, treatment, and outcome. Specifically, it deals with past and current diagnostic criteria for juvenile onset bipolar disorder, the controversy around its comorbidity with attention deficit hyperactivity disorder (ADHD), and how to differentiate it from ADHD, conduct disorder, drug and alcohol abuse, and schizophrenia, Genetic and neuroimaging studies investigating the possible etiology of this condition are also described. Treatment, both pharmacological (eg, lithium, neuroleptics, anticonvulsants, benzodiazepines, antidepressants) and psychosocial (eg, psychoeducation of child and family, school intervention, family, group and/or individual therapy) are outlined. Finally, long-term outcome and factors which may influence outcome are addressed.