Diabetic neuropathy is a dying-back polyneuropathy with distal degeneration of the longest nerve fibers advancing in a centripetal direction. Multiple histopathological changes are observed, but progressive fiber loss is the hallmark of diabetic polyneuropathy. Other important features include endothelial cell basement membrane thickening, segmental demyelination and remyelination, and axonal atrophy. Similar pathological changes are observed in type 1 and type 2 diabetes. The severity of neuropathy as indicated by the stage of nerve fiber loss determines the clinical, electrophysiological, and quantitative sensory threshold features of this disorder. The functional measures of electrophysiological and quantitative sensory thresholds reflect the morphological changes and the clinical features.