Since the DSM-III, the category of dysthymia includes patients that were previously considered as neurotic, reactive, characterological, temperamental, minor or atypical depressives as opposed to a category of endogenous, autonomous, morbid, major or typical depressives. Despite certain confusion, the need for a nosological category is very important for patients suffering from years of depressive mood, with a significant impact on their life-styles and adaptation, as they can benefit enormously from modern antidepressant treatments. DSM-IV and ICD-10 describe dysthymia in a very similar way although there are significant differences. The differences are the consequence of the lack of sufficient scientific data in some points and the need to take a decision, but also to indicate areas for future research. Other differences are the consequence of major discrepancies in basic perspectives of the classifications (ie, the importance given to disablement for the diagnosis). The similarities between both classifications allow the use of either of them for most purposes. Research on the different classifications should help in better defining the concept of dysthymia and mood disorders in general (ie, the cut-off points between them) and of psychiatric nosology.