Diagnostic reliability receives cursory attention in the literature with wide ranges of kappa coefficients often interpreted as “adequate.” Moreover, the vast majority of personality disorder (PD) kappa estimates, including those reviewed by Flory (this chapter), are derived from the audio/video recording method. This method results in inflated estimates of diagnostic reliability, which provides limited insight into whether patients would receive the same diagnosis at different hospitals or clinics and whether researchers are studying similar patients. A more rigorous and ecologically valid method for assessing diagnostic reliability is the test-retest method. Although echoing some of Flory’s points, the authors here disagree with her assertion that categorical PDs demonstrate acceptable reliability. In fact, the reliability of categorical PDs assessed using the test-retest method is far lower than the DSM-5 conceptualization would indicate. Moreover, the test-retest diagnostic reliability of categorical PDs fails to achieve minimal benchmarks established in the “normal” personality literature, indicating critical problems for the DSM-5 categorical model. If the goal is to provide optimal patient care and advance clinical science, then adopting the trait-based dimensional model of personality pathology from section III of DSM-5 is necessary.