This article starts with a discussion of the somewhat paradoxical character of the concept of ‘lay diagnosis’, as it suggests that lay persons could fulfill such a specific professional task. It is used here as indicating any kind of verbal contributions patients could make to the diagnostic process. Within the research on doctor–patient interaction, two different trends are distinguished, one focussing on how physicians' behavior is inviting, allowing, or discouraging patients from expressing their ideas and feelings, while the other presents an overall structural view of medical encounters ‘as a genre’ in itself. The latter perspective is elaborated at some length as offering at least a partial elucidation of the findings of the first concerning the effects of physicians' conduct of the consultation. The interactional significance of ‘lay diagnostic’ contributions seem to differ according to the phase of the consultation in which they are offered. In the conclusions, some implications for future research and practice are suggested, including an extension of the research agenda to include both pre- and post-clinical lay discussions of diagnostic concerns.