Relationship betrayals, such as sexual and emotional infidelity, are commonly encountered in the practice of psychotherapy, yet clinicians often report difficulties in assessing and treating them. In this article we offer suggestions for assessing relationship betrayals. We address the definition of relationship betrayals, methods of assessing relationship betrayals, when and whom to assess, confidentiality, and assessing related clinical concerns. We illustrate with case vignettes the assessment and treatment of betrayals in close relationships.