Previously bipolar disorder had been acknowledged as a relatively rare disease seen during pediatric, and adolescent age groups, however nowadays increases in the number of children with the diagnosis of bipolar disorder have gradually emphasized the importance of definition, classification, and management of this disorder. Incidence of bipolar disorder in children younger than 10 years of age is very low (0.3-0.5 % of all the cases with bipolar disorder) however prominently increased rates of incidence have been reported for the adolescent period. In this article, we analyzed an early- onset bipolar disorder diagnosed in a 10–year-old patient. This case has been presented upon establishment of diagnosis based on psychiatric examination, and interviews, DSM-4 TR criteria, and then psychometric test results. An 8–year-old female patient was referred to our outpatient clinic upon complaints of insomnia, an incessant urge to shopping, exertion of violence on her friends, defying their parents, abusive talking, aggressive behaviours, and talking a lot as expressed by her attendants and hospitalized with an initial diagnosis of manic episode. Consequently, the patient was followed up with an early- onset bipolar disorder and brought for the first time to an external outpatient clinic of pediatric psychiatry when she was 8 years old, with complaints of hyperactivity, poor school performance, stubbornness, difficulty in separating from her mother, and waking from sleep crying. She had been followed up in that center for 2 years with the diagnosis of attention deficit hyperactivity disorder (ADHD). After diagnosis of bipolar disorder had been made, the attendants said that she had been hospitalized for 7 times, and her self-care had deteriorated gradually between manic episodes. The patient, who had been diagnosed to have ADHD, when she was 8, had experienced her first manic episode at age 10. She has been currently followed up with the diagnosis of early-onset bipolar disorder. Establishment of a diagnosis of bipolar disorder in adolescence, and childhood is a very challenging issue in that its symptoms progress silently or differ widely from classical mania together with overlapping of their symptoms with manifestations of other mental disorders more frequently seen in the pediatric age bracket. Diverse diagnostic, and assessment criteria determined for pediatric, and adolescent mood disorders further complicate this diagnostic decision-making process. Corroborative efforts for the establishment of diagnosis, and treatment will disclose difficulties encountered in the diagnosis and management of early-onset bipolar disorder, and contribute to the development of a common algorithm for its diagnosis, and treatment.