Psychological assessment relies on accurate and forthright reporting to determine valid clinical presentations. However, it has long been recognized that examinees may be motivated to present a "better picture" through Positive Impression Management (PIM). Within the PIM domain, two distinct motivations (i.e., defensiveness and social desirability) emerge that have not been clearly differentiated in empirical literature. This thesis addressed the research gap for detecting PIM distortion of personality pathology, utilizing the Personality Inventory for DSM-5 (PID-5). In this investigation, 106 psychiatric inpatients were recruited from the adult Co-Occurring Disorders and Trauma Programs at University Behavioral Health. Using a mixed within- and between-subjects design, participants engaged in simulation via scenarios to be considered for a highly valued rehabilitation program (defensiveness) or employment (social desirability). As expected, inpatients showed elevated levels of problematic personality traits when reporting genuinely, but suppressed them under PIM conditions. These findings highlight that the PID-5, like all multiscale inventories, is highly vulnerable to intentional PIM distortion. Interestingly, respondents in the social desirability condition generally engaged in more total denial than those in the defensiveness condition. Empirically- and theoretically-based validity scales were developed to identify simulators and differentiate between conditions. Besides PIM, higher levels of experienced stigma were associated with more personality pathology, particularly the domain of Detachment. In addition, ancillary analyses showed strong convergence of the PID-5 with its hierarchical trait model to the DSM-IV categorical model. Continued research to detect PIM distortion, and more importantly to differentiate between PIM motivations, is essential for accurate clinical assessment of personality disorder traits and effective treatment planning.