Early onset depression, regarding its high prevalence and debilitating effects on development, is considered to be one of the major mental illness in children and adolescents. Most commonly is recurrent and continues in adulthood. Factors determining vulnerability to depression can be grouped into following categories: genetics, familial environment, personal characteristics and severe stress. Main risk factors include: being a female, family history of depression, subclinical symptoms, negative cognitive style, negative life events. Common symptoms of depression can be different in children and teens than they are in adults. Often occur with atypical features. The diagnosis might be problematic as it often relays on the observation of children's dysfunctions. Therefore treatment of major depression in children and adolescents is considered difficult. It is important to estimate all the features that underlie the symptoms, their persistence, and then implement proper therapy.