Diabetes mellitus is a disorder in which the concentration of blood glucose is persistently raised above the normal range. It occurs either because of a lack of insulin or because of the presence of factors which oppose the action of insulin. Hyperglycaemia results from insufficient insulin action. There are many associated metabolic abnormalities—notably, the development of hyperketonaemia when there is a severe lack of insulin, together with alterations of fatty acids, lipids, and protein turnover. Diabetes is a permanent condition in all but a few special situations in which it can be transient.

A wide variety of disturbances affecting the central and peripheral nervous systems, either directly or indirectly, may be encountered in patients with diabetes mellitus. This short selective review concentrates on recent progress in the delineation of the clinical features of the neurological syndromes related to diabetes and their management. It will deal, sequentially, with the classification of diabetes, a listing of some genetic disorders that may be accompanied by diabetes, the consequences of acute metabolic decompensation, and somatic and autonomic neuropathies, cerebrovascular disease, certain infections that have a particular association with diabetes and, finally, congenital malformations.