Purpose: This study tested key psychometric properties of the Older Adult Psychological Abuse Measure (OAPAM), one self-report scale of the Older Adult Mistreatment Assessment (OAMA). Design and Methods: Items and theory were developed in a prior concept mapping study. Subsequently, the measures were administered to 226 substantiated clients by 22 elder abuse staff from 7 agencies in a full-scale field test. The resulting database was used to estimate the psychometric properties of the OAPAM using the Rasch item response theory model and traditional validation techniques. Analyses included tests for dimensionality, model fit, and theoretical construct validation. Results from the OAPAM client report were validated against the adult protective services substantiation decision of abuse and the elder abuse staff assessment of psychological abuse (PA). Results: The client self-report measures met stringent Rasch analysis fit and unidimensionality criteria and had high person (internal consistency) and item reliability. The validity results supported the usefulness of the client measures and led to reconsideration of aspects of the hypothesized theoretical hierarchy. A short form was developed. Cut-points were proposed to distinguish levels of PA. Implications: The measure is now available to aid in the assessment of PA of older adults by both clinicians and researchers. Theoretical refinements developed using the Rasch item hierarchy may help to improve assessment and intervention.