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. Another form of display is also disclosed which illustrates administrations of a pharmacological agent and corresponding measurements of the patient's condition, with a visual link such as colour-coding linking the administration to the corresponding condition measurement. For example several days of insulin administration dosages may be displayed alongside several days of blood glucose measurements, with the administrations colour-coded to the corresponding blood glucose measurement, to assist the patient in determining whether the insulin administration is stably controlling their condition.