Objective: Research has raised questions about the ability of clinicians to make reliable diagnostic judgments about personality. The aim of this study was to assess the reliability and validity of the dimensional diagnosis of pathological personality traits with the Shedler-Westen Assessment Procedure-200 (SWAP-200) Q sort. Method: Two clinician/judges independently described 24 outpatients using the SWAP-200, based on a systematic clinical interview. Treating clinicians described the patients using the SWAP-200 based on their knowledge of the patients over the course of treatment while they were blind to interview data. Results: Interrater reliability was high. Convergent and discriminant validity between interviewers and clinicians was also strong. A procedure recently developed for providing precise estimates of construct validity with contrast analysis applied to correlational data documented strong evidence of validity. Conclusions: Clinicians and independent interviewers can reliably assess complex personality traits associated with personality pathology using the SWAP-200.