Personality disorders are not granted the same clinical attention accorded Axis I disorders despite their instrumental role in treatment and outcome. Even when standardized assessments are used, their clinical utility may be limited by an overly favorable self-presentation. The current study focused on defensiveness, the intentional denial of symptomatology, by examining individuals’ ability to minimize their presentation on personality disorder diagnostic measures. Using a within-subjects simulation design, dually diagnosed inpatients were assessed under both honest and defensive conditions. The study used self-report (Structured Clinical Interview for DSM-IV – Axis II – Personality Questionnaire, SCID-II-PQ) and interview-based (Structured Interview for DSM-IV Personality, SIDP-IV) diagnostic measures and a self-report measure of favorable self-presentation (Paulhus Deception Scales, PDS). The inpatients were quite capable of hiding maladaptive personality traits on diagnostic measures, with similarly large effect sizes on both the SCID-II-PQ and SIDP-IV. In addition to the PDS, two new detection strategies for identifying defensiveness showed promise.