Medical researchers and ethicists emphasise the importance of equity, fairness and justice in general medical research participation. No individual or group should be over-represented or under-represented in research—there should be fair participation. Thus far little thought has been given to fair participation in medical education research. There is no evidence based answer as to whether vulnerable groups are ever exploited in medical education research, or whether other individuals or groups are overlooked. However the heavy reliance on undergraduate learners as subjects for medical education research creates two key threats to the fairness of that research. First, there is a risk that undergraduate learners, as a potentially vulnerable population, may be exploited in research settings. Often the faculty carrying out medical education research will be the same faculty that are responsible for delivering medical education and assessing medical students’ competencies. It is possible as a result that medical students might feel pressured to participate in research. Second, there is a risk that other important groups of learners may be inadequately represented. Much medical education research is carried out on undergraduates and relatively little on those who have been doing CPD for many years. Thus much of our research concentrates on only a small proportion of medical learning. The relatively small amount of research carried out on those doing continuing professional development (CPD) is probably because of the difficulties of recruiting and retaining this group of learners in research programmes.