Despite the importance and the ubiquity of medical patient information in many healthcare systems in the world, we know very little about the lexical characteristics of the register. We do not know how patients perceive the information in the leaflets or whether the messages are transmitted effectively and fully understood. How a medical authority instructs and obliges patients in written information is also unclear.While the number of radiographic examinations performed globally increases year on year, studies consistently show that patients lack basic knowledge regarding the commonly-performed exams and show very poor understanding of the concomitant risks associated with radiation. There is, then, a pressing need to investigate radiography patient information in order to better understand why, and where, it is less effective.This thesis applies three approaches common to the field of corpus linguistics to uncover some of the lexical characteristics of patient information for radiography. The approaches used in this thesis are a keyword extraction, a lexical bundles analysis and an investigation of modal verbs used to express obligation.The findings suggest that patient information for radiography possesses characteristics more common to academic prose than conversation, although the high informational content of the register goes some way to explaining this and suggests that the reliance on these structures may, to a certain extent, be unavoidable. Results also suggest that the reliance on should to oblige and instruct is problematic as it may cause interpretation problems for certain patients, including those for whom English is not a primary language.Certain other characteristics of patient information revealed by the analyses may also cause comprehension, and while further research is needed, none of these characteristics would be evaluated as problematic by standard readability measures, furthering doubts about the suitability of such measures for the evaluation of medical information.An additional factor behind the increase in healthcare discourse studies is the huge rise in the use of the internet to search for healthcare information, to talk about healthcare both as a patient and as a professional, and to practise medicine. The ehealth or digital health market, which has a projected growth rate of more than 15% in the US, is driven by the prevalence of chronic diseases and government initiatives to deploy e-health (Grand View Research, 2018). In the UK, more than 80% of adults use the internet regularly with just over half reporting that they use the internet to search for health-related information, a figure that has grown by more than 30% over the preceding decade. (Office of National Statistics, 2018). The use of the internet for health reasons is of particular interest to language researchers who have studied patient-professional exchanges, including medical advice sites (e.g. Harvey, Locher & Mullany, 2013) as well as patient-patient communication via forums (e.g. Angouri & Sanderson, 2016; Seale, ...