Abstract: A method of displaying medical data, particularly data representative of the condition of patients suffering from chronic medical conditions such as asthma, diabetes and hypertension. The display consists of two graphical elements, one of which indicates the current value of a parameter indicative of the patient's condition, this being displayed against another graphical element which represents a model of normality for that patient. The graphical element indicating the current condition may be, for example, a needle, against a scale which is constructed according to the patient-specific model of normality. This is particularly advantageous in the case of displays which have a small display area, such as mobile telephones and PDAs. Other forms of display are disclosed, such as histograms with the display being dynamically colour-coded and auto-scaled, or displays including limits which may vary.