The Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5) and International Classification of Diseases 11th revision (ICD-11) have introduced a new dimensional approach to personality disorder (PD) classification that relies on the global level of PD severity and individual expressions of personality dysfunction in terms of specified trait domains (i.e., negative affectivity, detachment, antagonism, disinhibition, anankastia, and psychoticism). This study sought to evaluate the psychometric qualities of the DSM-5 and ICD-11 trait domains and facets in 570 Russian psychiatric inpatients using the Modified 36-Item Personality Inventory for DSM-5 and ICD-11 Brief Form Plus-Modified (PID5BF + M). The expected six-factor structure of the DSM-5 and ICD-11 trait domains was replicated using exploratory factor analysis. The six domain scores showed expected convergence with normal five-factor model scores, and the 18 subfacets showed acceptable scale reliability. Our findings overall support the psychometric properties of the six PID5BF + M domain scores and 18 subfacet scores covering both the ICD-11 and the DSM-5 trait models. Consequently, clinicians and researchers in Russian-speaking mental health services are now able to perform a combined and facet-level assessment of the DSM-5 and ICD-11 trait models in a feasible and psychometrically sound manner. (PsycInfo Database Record (c) 2023 APA, all rights reserved).