The practice of medicine has a long tradition of making a diagnosis by building up a composite picture of the symptoms and their history, a clinical examination and specialist investigations. A diagnosis enables the course of the disease to be predicted and the appropriate treatment used. However, scientific developments in genetics, by allowing us to detect specific abnormalities in chromosomes and in individual genes, are beginning to throw light on the mechanisms involved at a biochemical and molecular level. As a result the genetic and environmental factors involved in many disorders can be separated. This has heralded the birth of the practice of clinical medical genetics, a relatively new speciality in the wide and general field of medicine. With this development not only is there is a new understanding of diseases, but also an alteration in the way medicine is practised. The availability of newly discovered genetic knowledge, to all who want it, has necessitated a shift in the dynamic between the individual patient and the professional. The days have gone when the doctor was the benevolent patriarch knowing the secrets of diseases and administering to the patient, the grateful receiver. Today, people want to take personal responsibility for their health and are encouraged to do so. There is a general interest in understanding health matters and a common desire to know about medical matters and this is validated by the individual's right of access to personal information. The individual now has choice.