While a large body of conversation analytic research focuses on talk in medical settings, a relatively small but important emerging body of research on that subset of medical problems which affect individuals’ ability to produce and comprehend language has been developing. This paper reviews such research on four such medical problems: aphasia, Autism Spectrum Disorder, intellectual disability, and forms of dementia such as Alzheimer’s. This research provides useful insight into the nature of symptoms and the actual communicative competence of the individuals affected, as well as improving our knowledge of the best ways to diagnose, assess, and treat these conditions.