[To be continued][long dash]Neurologic disorders are a common and often disabling aspect of diabetes mellitus. Pain and sensory disturbances, weakness and paralysis and symptoms of autonomic dysfunction may be experienced by the diabetic patient. Although neurologic disorders have been noted in association with diabetes mellitus for many years, knowledge concerning this group of disorders is quite incomplete. Terminology used in discussing them is often vague and inconsistent. There is no accepted method of classification. Pathologic studies are incomplete and inconclusive. A great variations in clinical manifestations creates difficulties in diagnosis as well as in pathophysiologic interpretation. Numerous papers have discussed the theories of pathogenesis of these disorders, yet none has answered the basic question. This report is a review of a major portion of the literature on the subject. Emphasis is placed on the theoretical as well as practical aspects of these disorders, as their relationship to the disease state of diabetes mellitus is unique and important. These disorders must be explained in a final analysis of diabetes mellitus. Deficiencies exist in the present state of knowledge, but a solid basis for future study has been established.