The Five-factor model (FFM) provides a viable dimensional model of personality disorder assessment. Advantages of the FFM include the provision of a precise yet comprehensive description of both normal and abnormal personality functioning, the avoidance of the many limitations and problems inherent to the categorical diagnostic system, and the incorporation of basic science research on general personality structure and functioning into clinicians' description and understanding of personality disorders. We discuss three alternative instruments for the assessment of personality disorder from the perspective of the FFM. We also provide a method for diagnosing personality disorders and illustrate its application through a case study.