A clinical picture of bipolar affective disorders in children and adolescents is variable and dependent on the specificity of developmental age. From diagnostic and therapeutic point, especially difficult are cases with the pre-pubertal onset. In the article, a case report of 18-year observation of male patient with the onset of bipolar affective disorder at 11 years of age is presented. This very early pre-pubertal onset of the illness was manifested with rapid cycling, depressive episode with psychotic symptoms and the classic symptoms of mania. The use of lithium carbonate appeared effective and safe. Lithium was used for two years in combination with valproates, and in following years as monotherapy. In recent two years, due to depressive episodes of moderate intensity, the patients also received fluoxetine on periodic basis. No adverse effects of the treatment were observed.