We describe the application of fundamental moral principles, with particular emphasis on prima facie duties, to formal codes of ethics that regulate the conduct of forensic psychologists who act as expert witnesses. Then we discuss the American Psychological Association's "Ethical Principles of Psychologists and Code of Conduct" and the Committee on Ethical Guidelines for Forensic Psychologists's "Specialty Guidelines for Forensic Psychologists" and critically appraise how these documents translate basic moral principles. We conclude that, in many ways, the documents exemplify ethical (...) obligations such as nonmaleficence, beneficence, and justice, but they fall short in many other ways, particularly with regard to autonomy and fidelity. (shrink)