This article reviews naturalistic and controlled studies of the impact of comorbidity of personality disorders and depression on response to various forms of treatment. The findings support the common belief that personality disorders are associated with a poorer response to treatment for depression. In contrast, the limited data available suggest that the presence of depression may be a positive prognostic indicator for patients with borderline and antisocial personality disorder. There are insufficient data to draw conclusions regarding the influence of specific types of personality disorders on outcome with specific forms of treatment for depression. More specific assessment of personality disorders, particularly of possible underlying dimensions, is likely to be a more fruitful approach than the currently used categorical approach in identifying effective treatments for patients with personality disorders and depression.