An active line of current investigation is how the five-factor model (FFM) of personality disorder might be applied by clinicians and particularly, how clinically useful this model is in comparison to the existing nomenclature. The current study is the first to investigate the temporal consistency of clinicians' application of the FFM and the DSM-IV-TR to their own patients. Results indicated that FFM ratings were relatively stable over 6 months of treatment, supporting their use by clinicians, but also indexed potentially important clinical changes. Additionally, ratings of utility provided by the clinicians suggested that the FFM was more useful for clinical decision-making than was the DSM-IV-TR model. We understand the clinical utility findings within the context of previous research indicating that the FFM is most useful among patients who are not prototypic for a personality disorder. Copyright © 2010 John Wiley & Sons, Ltd.