Objective: Mania in children and adolescents had been rarely diagnosed until recently. In this article, it is aimed to provide a review of epidemiology, clinical course, neurobiology, comorbidity and differrential diagnoses of child and adolescent bipolar disorder. Method: Published literature which are earlier and recent relevant articles were used. Many of these articles raise questions of diagnosis and differential diagnosis of bipolarity in childhood and adolescence. Results: Age-specific, developmental clinical manifestations, episode and course features, comorbidity and differential diagnoses (especially disruptive behaviour disorders) were discussed. Conclusion: The data obtained from related articles suggest that early-onset bipolar disorder is a non-episodic, chronic, rapid-cycling, mixed manic state that may be interfere with attention deficit hyperactivity disorder. For that reason, early-onset form. Besides, with appropriate diagnosis and treatment, and profilactic medicine treatment, this group will be protected from a more severe condition