Objectives: We aimed to determine which, if any, features distinguish antisocial and narcissistic personality disorders (ASPD and NPD), two overlapping externalizing disorders.Methods: A large sample of outpatients (N = 2,149) completed interview measures assessing personality pathology, other psychopathology, and impairment. The structure of antisocial and narcissistic traits was examined using both exploratory bifactor and traditional exploratory factor analytic approaches, and we examined relations for our emergent factors.Results: Factor analytic results indicated that most narcissistic and antisocial traits were strongly overlapping, although some features emerged as relatively distinct (e.g., arrogance defining NPD). Factors modeling our specific bifactor dimensions showed very weak psychopathology and impairment relations. Conclusions: The structure of ASPD and NPD traits does not align neatly with Diagnostic and Statistical Manual of Mental Disorders (DSM-5) Section II conceptualizations, Regardless of the factor analytic approach used. Our findings also indicate that specific dimensions defining these PDs show modest predictive power after accounting for a general externalizing dimension. K E Y W O R D S assessment, externalizing, factor analysis, personality disorders, transdiagnostic J. Clin. Psychol. 2019;75:433-444.wileyonlinelibrary.com/journal/jclp