["Journal of Clinical Psychology, EarlyView. ", "\nABSTRACT\n\nObjectives\nThis study assessed the Czech version of the Inventory of Personality Organization (IPO‐CZ) in relation to borderline personality disorder (BPD) as defined in the ICD‐11 model for PDs and defensive functioning in BPDs. The IPO‐CZ was used as a proxy measure of personality functioning (PF), although not fully identical to the conception of PF within the ICD‐11 framework defined by the severity of self‐other impairment.\n\n\nMethods\nThe IPO‐57, Borderline Personality Questionnaire, and Defense Style Questionnaire were administered to general population volunteers (n = 371) and mixed psychiatric patients (n = 293).\n\n\nResults\nThree‐factor solution of the IPO‐CZ (i.e., Instability of self and others [ISO]; Instability of goals and behaviors [IGB]; and Psychosis) was confirmed, to a large extent reflecting Kernberg's initial concept of personality organization. Since the measurement invariance of the 57‐item version was not confirmed across samples, a 14‐item version of the IPO‐CZ was developed. ISO was strongly associated with 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 used.\n\n\nConclusion\nWhile ISO appears to be an indicator of PF in terms of general self‐other disturbance, IGB may be considered a specifier of the defense mechanism‐based management of impulsive aggression typical of BPD patients that should not be ignored. Moreover, the study found measurement invariance across general and clinical sample for IPO‐14.\n"]