This paper reports a critique of the literature of problem-based learning (PBL) in medical education. The objective of the review was to examine the various meanings that medical teachers attribute to concepts of adult learning and self-directed learning within the context of PBL. The critique found that there are assumptions about the meanings of adult learning and self-directed learning that are accepted uncritically as appropriate to PBL. The nature and the origins of teachers' conceptions of these ideas are explored in an attempt to clarify the meanings of the concepts and the relationships amongst them. An alternative meaning for self-directed learning in PBL curricula is proposed.