The varied course of evolution of personality disorders (PD) and patients’ different responses to therapeutic interventions position the concept of severity of PD amongst the greatest concerns to clinicians and researchers. In a previous study (Ramos, Sendra, Sánchez, & Mena, 2015) we proposed an index of severity of PD based on the overlap of pathological traits; now we analyze the change in severity after 6 months of specialized treatment. In 93 patients who completed the program (51.4% of the total sample) we found a reduction in general (d= 1.193) and affective (d= 0.990) disturbance, also in PD traits and severity (d= 0.753). Nevertheless, interaction effects between change and severity did not appear; neither did severity by itself predict therapeutic results. We discuss the data in the light of other findings. The stability of the PD does not seem to reside in the fulfillment of diagnostic criteria, but in a core of vulnerability shared by all the patients, independently of the prototypical categorization and the symptomatology fluctuation.