Numerous epidemiological and clinical studies found a high incidence of comorbidity in children and adolescent psychiatry. In population of children and adolescents is most often described and researched comorbidity of depression, anxiety disorders, than in hyperkinetic and behavioral disorders, and finally the difficulty in reading (dyslexia) and antisocial behavior disorders. The common occurrence of two diagnoses may be the result of a disorder that has a complex pattern of symptoms, which apparently seems to be two disorders, but in fact is a single disorder. Comorbidity may be two disorders that share the same set of risk factors or is it possible that a one disorder is a risk of development of other disorder. Knowledge and understanding of comorbidity is important as a preventive and therapeutic point of view. Comorbidity is particularly important because complicates diagnostic process and influences the course, prognosis and treatment of children and adolescents.