Objectives: Defining bipolar disorder in children is a topic of multiple debates. DSM-IV criteria can not cover all clinical phenotypes. This paper represents a literature review on this topic. Method: In a review study, data were collected through searching in relevant databases and assessing available texts. Results: Developmental processes may change clinical presentation of bipolar disorder in children. Comorbidity with other disorders and normal childhood phenomena adds to the diagnostic debates. Atypical presentation appears to be the common clinical picture of bipolar disorder in childhood. Its premorbid symptoms, longitudinal course and continuity to adulthood are still not completely understood. Some investigators have proposed three clinical phenotypes for childhood bipolar disorder. Wide researches are trying to evaluate the validity of broad phenotype bipolar disorder or" severe mood dysregulation". Conclusion: Defining clinical phenotypes is important in planning the treatment and anticipating the course and prognosis of the illness. The diagnostic subtyping will have higher validity if based on data from multiple sources namely phenomenology, course of illness, biological markers, familial clustering, and treatment response.