Dysthymia and chronic depression: introduction, classification, risk factors, and course.

Chronic forms of depression are more common and impairing than is generally recognized. This article introduces an In Session issue devoted to dysthymic disorder and chronic depression, and it reviews current knowledge about these disorders. First, we discuss nosological issues, followed by a summary of potential risk factors. Finally, the naturalistic course of chronic depression is described and implications for clinical practice are discussed.