Romney and Bynner (1989) demonstrated by means of structural equation modeling that five of the DSM-III personality disorders fitted around a circle. These five were narcissistic, paranoid, schizoid, dependent, and histrionic. In the current study the five other personality disorder-antisocial, borderline, avoidant, passive-aggressive, compulsive-were found to fit a simplex model. This model represents a linear ordering of the disorders along a single dimension, Impulsiveness, ranging from most impulsive (antisocial personality disorder) to least impulsive (compulsive personality disorder). The finding that these five disorders can be ordered sequentially according to their degree of impulsiveness is consistent with what is known about their clinical features. Furthermore. Impulsiveness may be considered to be a mixture of Neuroticism and (lack of) Conscientiousness, two of the Big Five dimensions of personality that do not define the interpersonal circumplex.