Research on Criterion A of the alternative model for personality disorders is recently expanding and provides mixed results concerning the unidimensional operational definition of severity by the model, characterized by impaired self (identity and self-direction) and interpersonal (empathy and intimacy) functioning. Studies resulted in one, as well as two or more factor structures. The present study demonstrated the importance of the structural and relational differentiation of self and interpersonal dimensions of personality functioning. One thousand seventy-four participants (community and clinical mixed sample) completed the Level of Personality Functioning Scale - Brief Form 2.0 (LPFS-BF 2.0), the Personality Inventory for DSM-5 Short Form and the Questionnaire for the World Health Organization Disability Assessment. An LPFS-BF 2.0 two-factor structure with self and interpersonal functioning factors was corroborated by confirmatory factor analyses and bifactor modeling. Joint Exploratory Factor Analysis of the LPFS-BF 2.0 domains with maladaptive personality domains clearly differentiated the personality functioning factors. While the self-functioning factor was more closely linked to negative affect (and to disinhibition and psychoticism), the interpersonal functioning factor connected to detachment. Self-functioning predicted functional impairment along and beyond personality domains. The LPFS-BF 2.0 appears a useful tool for clinical routine monitoring of both self and interpersonal functioning.