Dysthymia or persistent depressive disorder is an affective disorder of chronic course and lower intensity than major depression. Its onset is insidious and usually appears in youth. The presence of a depressed mood for at least two years, along with other symptoms such as sleep disturbances, low self-esteem, poor concentration or fatigue are features of this disorder. Sometimes, major depressive disorder is superimposed on an underlying dysthymia («double depression»). Diagnosis is clinical, being essential differential diagnosis from other entities (major depression, personality disorders, substances and drugs abuse). Combination of antidepressants and psychotherapy is the most effective treatment.