Ischaemia of the deep subcortical white matter in the brain may be a common contributor to disability and cognitive impairment in old age. There is tremendous potential for preventing, or at least slowing, some of this damage. However, progress both in research and in clinical practice has been hampered by the confused nosology, with various diagnostic and descriptive labels applied to appearances on neuroimaging, to the underlying pathology and to clinical states (Table 1).