In his 1910 report on medical education, Flexner emphasized the importance of competency in basic sciences. Less widely recognized is that he also emphasized the necessity of liberal education. On the Flexner Report's 100th anniversary, medicine is challenged to realize Flexner's full vision for medical education to ensure that physicians are prepared to lead lives of compassion and service as well as to perform with technical proficiency. To meet the complex medical and social challenges of the next century, medical educators must continue to promote cognitive expertise while concurrently supporting "professional formation"-the moral and professional development of students, their ability to stay true to their personal service values and the core values of the profession, and the integration of their individual maturation with growth in clinical competency. The goal of professional formation is to anchor students to foundational principles while helping them navigate the inevitable moral conflicts in medical practice. The consequences of inadequate support for professional formation are profound, impacting individual learners, patients, the profession, and society at large. Among the many successful professional formation projects nationally, two long-standing programs are described in modest detail to identify common elements that might guide future developments elsewhere. Key elements include experiential and reflective processes, use of personal narratives, integration of self and expertise, and candid discussion within a safe community of learners. Committing to professional formation within medical education will require transformation of formal and informal curricula and will necessitate a rebalancing of attention and financial support within schools of medicine.