Researchers have proposed replacing the current system for diagnosing personality disorders with a dimensional trait model. Proposed trait models have been derived primarily from data provided by untrained lay informants (often via self-report questionnaires) using item sets derived from lay conceptions of personality. An alternative is to derive personality trait dimensions from data provided by clinically expert informants using an instrument that includes personality features salient to clinicians who treat personality dysfunction. The authors report the factor structure of the latest edition of the Shedler-Westen Assessment Procedure (SWAP-II) using a normative clinical sample of 1,201 North American patients assessed by experienced psychologists and psychiatrists. Factor analysis identified 14 clinically and empirically coherent factors. The findings highlight dimensions of personality and personality pathology that have not emerged in personality item sets designed for lay personality description.