Diabetic polyneuropathy is etiologically related to prolonged hyperglycemia with multiple consequences. Although strict glycemic control prevents neuropathy in type 1 patients if maintained for many years, similar interventions in those with type 2 diabetes mellitus are less successful. Type 2 patients may have neuropathy with considerable nerve fiber loss at the time of diagnosis because of unsuspected hyperglycemia in preceding years. Reversal of established neuropathy with strict glycemic control is not certain to occur, even if maintained for many years. Co-morbid disease often interferes with strict management of type 2 diabetes. Even among those with type 1 diabetes, a minority of patients are successful in maintaining prolonged euglycemia.