The aim of this review was to identify the strengths and weaknesses of the roles of real and simulated patients in undergraduate medical education. The literature was reviewed in relation to four patient roles: real patients as educational "resource" (passive role), real patients as teachers (active role), and simulated patients as educational resource and teachers. Each of the four patient roles was found to have specific advantages and disadvantages from the perspectives of teachers, students, and patients. For example, advantages of real patients as educational resource were patient-centered learning and high patient satisfaction. Disadvantages were their limited availability and the variability in learning experiences among students. Despite the considerable amount of literature we found, many gaps in knowledge about patient roles in medical education remain and should be addressed by future studies.