The literature pertaining to the stability and course of personality disorders is briefly reviewed. Available data suggest that PD diagnoses demonstrate only moderate stability and that--although generally associated with a plethora of negative outcomes--they can show improvement over time. This paper highlights the pervasiveness of diagnostic co-occurrence and its implications for continued investigation of the question of PD stability. In addition to examining the stability (and outcome) of PDs, longitudinal studies need to consider continuities between diagnoses. The Collaborative Longitudinal Personality Disorder Study (CLPS) is described briefly vis-a-vis some of these major issues.