An AAMC working group concluded that medical educators have paid insufficient attention to students' development of professional standards and to the immediate ethical dilemmas that students face as students. Its discussion of the primary determinants of medical students' ethical development focused on improving: (1) the evaluation of candidates for admission; (2) the medical school learning climate, including recognition of the challenges inherent in the increasing cultural diversity among students and patients; and (3) communication to students of expectations of professional behaviors and standards. An AAMC initiative is outlined that includes preparation of a resource book featuring cases illustrating common ethical dilemmas that medical students face, descriptions of effective honor systems, suggestions for faculty development, and an annotated bibliography.