In the past decade, at least four sets of ethics guidelines for epidemiologists have been prepared by various national and international organizations. None, however, have been officially adopted by the American College of Epidemiology (ACE). Recently, the ACE asked its Ethics and Standards of Practice (ESOP) Committee to produce ethics guidelines. In this paper, we explain the context and rationale for this effort, describe the purpose and content of ethics guidelines in epidemiology, and discuss their strengths and weaknesses. Three issues that are central to the mission of ACE-education, policy, and advocacy-are inadequately addressed in existing ethics guidelines. In addition, ethics guidelines are not static documents; they should reflect the changing role of epidemiologists in society, including issues arising in emerging subspecialty areas. New, more dynamic, guidelines that emphasize core values, obligations, and virtues, may help to further define and legitimize the profession of epidemiology and will provide a foundation for the discussion of specific ethical issues in the classroom and in professional practice. Guidelines however, do not provide the final word on ethical issues. Specific decisions in particular cases require judgments made upon reflection of the core values, obligations, and virtues described in the guidelines. From our review, we conclude that a new set of guidelines is reasonable and warranted.