Recently, the Korean Neuropsychiatric Association expelled one of its members on grounds of multiple ethical violations, which included a sexual boundary violation between doctor-patient relationships. However, the lack of understanding of why this is an ethical issue was found among the general population as well as psychiatric professionals. In this review article, we introduce the basic concepts of psychotherapy and psychiatrist-patient relationships, including therapeutic structure and transference/countertransference, and elaborate the reasons why boundary violations, and especially sexual boundary violations, are unethical and potentially harmful to the patient and to the psychiatric community.