Aims: The aim of the study was to develop a psychometric scale to reliably assess for psychosocial impairment following an experience of betrayal trauma. Method 434 participants from a community sample completed a series of self-report psychometric measures online of psychosocial impairment, betrayal trauma experiences and personality trait pathology. Results: The Betrayal Response Scale (BRS) consisted of 20 items and two subscales related to internalised negative emotions and negative interpersonal responses. Higher BRS scores were associated with personality pathology, interpersonal impairment and poor social functioning. Conclusion: The BRS is a reliable measure of psychosocial impairment following betrayal trauma. People with personality pathology report greater levels of psychosocial impairment following betrayal trauma. Potential uses of the BRS as a clinical and research instrument are discussed.