Certain personality traits or disorders in combination with clinical signs complicate the diagnosis and treatment of depression. The approaches to the relationships between personality and mood disorders vary. Some see important links between normal personality types (or temperaments) and depression, while others see certain temperaments as sub-syndromic variants of mood disorders. Finally, a third approach proposes an analysis, drawing on Robins and Guze's criteria, of the validity of psychiatric diagnoses for determining whether this frequent comorbidity of depression and personality disorders (DSM-III) is consistent with a nosologic relationship, or is merely some definitional or other artefact. A category-based diagnostic approach provides little clarification; in some studies, a dimensional model attempts to better define the links between depression, temperament and personality and clarify the content of the apparently heterogeneous notion of depression, with therapeutic implications. Research in this area should lead to the development of increasingly specific therapeutic approaches to depression.