The diagnosis and classification of personality disorders have come a long way since the beginning of the 20th century. Perhaps by this time next century, the diagnostic manual of mental disorders will be using a dimensional model of classification that will provide more reliable and meaningful points of demarcation between normal and abnormal personality functioning. This article offers suggestions for the form, content, and placement of such a dimensional model. The particular model emphasized herein is the five-factor model of personality functioning, but the optimal diagnostic system will probably involve an integration of alternative dimensional models.