Leukodystrophies are a group of rare, genetic diseases, which affect myelin, the major constituent of brain and spinal cord white matter. Patients suffer from numerous, progressive neurologic symptoms, which frequently cause death. The molecular defects causing leukodystrophies are heterogeneous. For some leukodystrophies the genetic cause is known, whereas for others the disease-causing gene has not yet been identified. Except for a few leukodystrophies, in which bone marrow transplantation is an option to prevent disease progression, curative therapy is not available. However, clinical trials involving gene therapy and enzyme replacement therapy have been initiated as a result of accomplishments in basic research. The development of magnetic resonance imaging and spectroscopy has improved the diagnosis of leukodystrophies. Nevertheless, due to the insidious and frequently non-characteristic onset of leukodystrophies and the fact that most primary physicians have never before encountered patients with these rare diseases, diagnosis is often delayed. In Germany, the Federal Ministry of Education and Research supports a network (LEUKONET), which aims to recruit most of the German leukodystrophy patients and, in addition, offers information for physicians, patients and relatives. All German clinical centers experienced in treating leukodystrophy patients participate in this network. The network also includes a number of basic researchers whose projects intend to elucidate the primary cause and pathogenesis of these disorders.