Dysthymic disorder (dysthymia) was introduced into the group of affective or mood disorders with the publication of the DSM-III in 1980. Although little was known of dysthymia at the time of its inclusion in this manual, subsequent research has resulted in a more detailed description of the phenomenology, epidemiology and associated comorbidity of the disorder.Accurate diagnosis of dysthymia remains difficult, being dependent on the recall of symptoms by patients. States of chronic mild depression, such as dysthymia, appear to be rather common, with a point prevalence of around 2 to 4%. Comorbidity with other psychiatric disorders is common, leading certain authorities to dispute the existence of ‘pure’ dysthymia.Although chronic mild depression is associated with considerable use of health service resources, and prescriptions of psychotropic drugs are common, the drug treatment of dysthymia has not been investigated extensively. Furthermore, methodological flaws characterise many of the existing published studies of treatments for the disorder.Nevertheless, recent research supports the use of antidepressant medication in certain groups of patients. Imipramine, certain selective serotonin (5-hydroxy-tryptamine; 5-HT) reuptake inhibitors and moclobemide may be of benefit, particularly in patients with ‘double depression’, in whom major depressive episodes complicate an underlying dysthymic disorder.