The virtues that constitute medical professionalism have been aptly described in multiple position statements from professional organizations and individuals. These professional virtues depend on particular moral community traditions to undergird and sustain them. Attempts to ground these virtues in narratives intrinsic to medical practice--in the moral consensus of physicians or patients, in the self-regulating character of medicine as a profession, in the Hippocratic tradition, or in the physician-patient encounter--have been unsuccessful. Modern medicine must, therefore, look outside its own methodological and clinical practices for grounding narratives sufficient to sustain the professional virtues set forth in the recently published professionalism statements. These professionalism statements are written to capture consensus, and they rarely acknowledge the external moral traditions on which the virtues depend, because doing so would, in a pluralistic culture, entail the risk of moral disagreement and division. The authors argue that meaningful education in professionalism must look beyond the consensus statements and deeply engage the particular cultural traditions external to the practice of medicine that sustain the professional virtues. Medical professionalism curricula should embody an open pluralism, giving voice to diverse moral communities, encouraging critical self-exploration and discussion about the truth claims of these communities, and, if possible, facilitating the integration of students' professional development with their ongoing participation in these communities. Engagement with and participation in these sustaining moral communities would promote the cultivation of virtue capable of withstanding the economic and social threats to professionalism that are inherent in modern medical practice.