Earlier factor analytical studies on the empirical validity of the DSM-IV-TR (American Psychological Association, 2000) Axis II classification have offered little support for the current three-cluster structure. In his large-scale meta-analysis of previously published personality disorder correlation matrices, O'Connor (2005) found four factors, corresponding to the neuroticism, extraversion, agreeableness, and conscientiousness domains of the five-factor model of personality. In the present study, this dimensional four-factor model and the categorical DSM three-cluster structure were fitted to the Assessment of DSM-IV Personality Disorders questionnaire (ADP-IV; Schotte & De Doncker, 1994) scale scores using structural equation modelling. The results strongly favored the dimensional model, which also resembled other well-founded four-factor proposals (Livesley, Jang, & Vernon, 1998; Widiger & Simonsen, 2005). Moreover, a multigroup confirmatory factor analysis showed that this model was highly invariant and thus generalizable across two large clinical (n = 1,029) and general population (n = 659) samples.