Objectives: This study tried to verify the predictive capacity of Inventory of Personality Organization (IPO) with respect to borderline personality disorder (BPD) as defined in the ICD-11 model for PDs and defensive functioning in BPDs. The IPO was used as a proxy measure of personality functioning, although not fully identical to the conception of personality functioning within the ICD-11 framework defined primarily by the severity of self-other impairment. Moreover, the study provides the first empirical test of the new 14-item IPO version. Methods: The IPO-57, Borderline Personality Questionnaire, and Defense Style Questionnaire were administered to general population volunteers ( n = 371) and mixed psychiatric patients ( n = 293). Results: Three-factor solution of the IPO (i.e., Instability of self and others (ISO); Instability of goals and behaviors (IGB); and psychosis) was confirmed, to a far extent reflecting Kernberg’s initial concept of personality organization. ISO showed to be the strongest predictor of self-other pathology in both samples, IGB showed to be an indicator of immature defensive functioning in both samples and mature-neurotic defenses in clinical sample when IPO-14 was applied. Conclusion: While ISO appears to be a good predictor of impaired personality functioning in terms of general self-other disturbance, IGB is a specifier of the defense mechanism-based affect management typical of BPD patients that should not be ignored.