Personality disorders (PD), by definition, are enduring and stable forms of psychopathology. This aspect is reflected in the general diagnostic criteria for PD in the Diagnostic and Statistical Manual of Mental Disorders – 5th Edition (DSM-5), which require that the maladaptive patterns of inner experience and behavior be “stable and of long duration” (p. 647). However, the accumulated results of several naturalistic studies indicate that DSM PD diagnoses and symptom counts do not exhibit a level of stability consistent with the clinical description of the phenomenon (Grilo et al., 2004; Lenzenweger, 1999; McGlashan et al., 2005; Zanarini, Frankenburg, Reich, & Fitzmaurice, 2012). This general finding was cited as a major reason for developing a revised system for characterizing and diagnosing PDs published in Section III (Emerging Models and Measures) of the DSM-5 (Skodol et al., 2011). Although past research suggests that dimensional assessments of PD traits are more stable than disorders or symptom counts (Hopwood et al., 2013; Morey et al., 2007; Samuel et al., 2011), the longitudinal (i.e., > 1 year) stabilities of the DSM-5 traits remain unknown. The current study was conducted to determine the mean-level, rank-order, and individual stability of the DSM-5 PD traits, as well as the longitudinal associations among traits and psychosocial functioning. Central to the concept of a PD is the enduring nature of the dysfunction, reflected in long-term persistent impairment. Although persistence is observed clinically, empirical findings paint a picture of considerable instability when PD diagnoses or symptom counts are followed prospectively using state-of-the-art empirical methods. In particular, the pattern of mean change is one of resolution or amelioration of symptomatology. For example, in the diagnoses followed in the Collaborative Longitudinal Personality Disorders Study (CLPS), 24-month remission rates ranged from 50% (avoidant PD) to 61% (schizotypal PD; Skodol et al., 2005). Similar findings have been observed in other studies (Cohen, Crawford, Johnson, & Kasen, 2005; Lenzenweger, 1999; McDavid & Pilkonis, 1996; Zanarini et al., 2013), and the same picture emerges when considering the more fine-grained changes associated with symptom counts as opposed to categorical diagnoses. In contrast, personality traits, including pathological traits (e.g., grandiosity, emotional lability), exhibit much higher rates of stability than PD symptoms (Clark, 2009; Hopwood et al., 2013; Morey et al., 2007; Roberts & Mroczek, 2008). Rank-order stability of traits is markedly higher when compared with dimensional PD symptom counts (Hopwood et al., 2013; Morey et al., 2007). Furthermore, although PD symptoms tend to remit over time on average, psychosocial dysfunction remains much more stable, likely accounting for the clinical observation of stability of impairment in PD (Skodol et al., 2005). Notably, both PD symptoms and personality traits have been shown to prospectively predict psychosocial functioning (Hopwood & Zanarini, 2010; Morey et al., 2007), although the effects are stronger for traits. Taken together, these findings have contributed to the strong evidence base showing the limitations of the existing diagnostic framework for PD, as well as the need to move to a model that would more closely match the basic definition of PD as a disorder characterized by longitudinal stability (Skodol et al., 2011). The DSM-5 currently presents two complete systems for diagnosing PD. The first, in Section II of the manual (Diagnostic Criteria and Codes), reflects only modest textual changes to the structure that has been in place since DSM-III. However, a second complete model reflecting major innovations is included in Section III (Emerging Models and Measures). This model includes a detailed description of PD-specific impairments (Criterion A) in the form of self- and interpersonal-dysfunction that replaces the general definition of PD, and a dimensional model of PD features (i.e., pathological traits) intended to map individual differences in PD expression (Criterion B). Remaining criteria reflect the standard requirements for pervasiveness (Criterion C), stability (Criterion D), and that the disorders are not better accounted for by other mental disorders, substances, or developmental stage (Criteria E, F, G). Although this model purports to address many of the documented limitations of the Section II model, these claims must be directly studied using the constructs and assessment instrumentation intended for use with the new model (e.g., the Personality Inventory for the DSM-5; PID-5; Krueger et al., 2012). In particular, the presumed benefit of bringing the empirical stability of PD features in line with the PD definition by switching to this trait model has not been tested. The current study had three primary aims. First, we sought to establish the stability of the DSM-5 Section III PD features (both primary traits and higher order domains) in individuals diagnosed with PDs over the course of 1.4 years. Our goal was to characterize both mean-level (i.e., normative) and rank-order stability, which are conceptually and quantitatively distinct. Second, we investigated whether the DSM-5 traits prospectively predicted psychosocial functioning. Finally, given prior research that has shown individual heterogeneity in PD and trait trajectories over time (Lenzenweger, Johnson, & Willett, 2004; Wright, Pincus, & Lenzenweger, 2011), we examined whether individual changes in psychosocial functioning were associated with individual changes in PD. This study is the first to examine the longitudinal performance of the DSM-5 Section-III PD model features and provides an important test of whether the putative benefits of adopting dimensional PD features in the new model are in fact evident when the model is implemented in patients diagnosed with PDs.