An increasing number of neurodegenerative diseases have been defined at the molecular level in recent years, making it possible to determine precisely the genotype before the onset of symptoms. Pre-symptomatic testing programs are available for Huntington disease (HD), hereditary cerebral haemorrhage with amyloid-Dutch type, inherited cerebral ataxia, myotonic dystrophy, and Alzheimer disease. Although treatment options such as gene therapy have no widespread application until now, and much has to be developed, the use of predictive DNA-diagnostics has become a clinical application for a number of hereditary diseases. For psychiatric disorders such as schizophrenia or bipolar disorders, there are indications for localisation of the genetic factors, but clinical use of genetics is still far from reality. Yet, the increasing knowledge about genetics will have far-reaching influence in most fields of modern medicine and in health care provisions.