This article gives an overview of the methodology used to study letters as sources for the history of medicine, describing the shift from a social to a cultural history of medicine, and its effect on the analysis of correspondence, based on both an overview of secondary literature and on the analysis of over 2,300 Dutch manuscript letters written by the Dutch elite from 1770 to 1850. The first part of the article outlines how the letter was used by social historians of medicine, who mostly concentrated on the contents of letters in regard to disease and patients' attitudes to physicians. Cultural historians, on the other hand, focus on the making of meaning and the second part of the article discusses how health and illness in letters may be analysed in terms of language use, omissions and a focus on the functions of correspondence, specifically on the performative use of letters.