Bipolar disorder (BD) is a relatively rare disease in childhood and adolescence. There is increasing recognition about bipolar disorder in childhood and adolescence because of poor therapeutic outcome and serious disruption of the development and emotional growth of the youth. The prevalence of bipolar disorder in prepubertal children has not been explored, however the prevalence in adolescence has been estimated to be approximately 1%. Bipolar disorder symptoms in children differ from symptoms in late adolescence and adulthood and this situation makes the diagnosis of BD complicated. The symptom overlap between ADHD and BD can create diagnostic problems and associate with poor prognosis. Early-onset bipolar disorder is a serious psychiatric disorder associated with social and academic difficulties, family dysfunctioning, relational difficulties with peers and suicidality. We have presented this case that we have considered to be early-onset bipolar disorder with ADHD. A 13-year-old male patient, with 7 years old symptoms such as, irritability, hyperactivity, inattendance to his school went under psychiatric examination and psychological testing and was diagnosed to have ADHD and mild mental retardation. Atomoxetine and risperidone treatment were prescribed. Then, the patient reported hearing of a sound, chuckles, delusions. These symptoms were associating with psychotic process. The patient was observed to have a constant religious ritual compulsion and talkativeness. Atypical Affective Disorder and Bipolar Affective Disorder were concluded and Sodium Valproate treatment was started. Patient’s symptoms partially reduced. It is rather difficult to identify BD in childhood and early adolescence. It is proposed that the reason of this difficulty is that BD is defined as non-cyclic or excessively rapid-cycling in this period and that it has common symptoms with ADHD like hyperactivity, distractibility or short duration of attention. The ADHD diagnosis made in our patients seems to be confirmatory for the difficulty in differential diagnosis of both disorders. All these opinions raise the debate whether the symptoms before the age of 7 years are the symptoms-related to ADHD or premising symptoms of bipolar disorder in our patient diagnosed as bipolar affective disorder. It has been proposed that childhood onset mania is a complex, continuous, rapid-cycling affective disorder which progresses with severe uneasiness and aggressive temperament crisis. Anger and uneasiness can be defined as prodromal symptoms in early-onset bipolar disorder. In our case, the main complaints were anger and aggressive temperament features when the parents presented to our clinic. Carlson suggested that uneasiness and emotional instability are detected in manic children younger than 9 years of age, while paranoia and grandiose delusions, euphoria and emotional surges in manic children older than 9 years of age. In fact, our patient also had grandiose delusion and paranoia. Bipolar affective disorder before puberty comprises an atypical clinical manifestation that progresses with short mania episodes as well as behavior and impulse control problems. The schizophrenia-like symptomatology should not mislead clinician and correct diagnosis should be made based on either personal or family history.