We investigated three diabetic patients whose neuropathy was characterized by pain, hypesthesia, and autonomic dysfunction, with preservation of epicritic sensation and muscle-stretch reflexes. Two sural nerves were studied qualitatively and quantitatively, using teased fiber, light, and electron microscopical techniques. The most striking alterations were encountered in unmyelinated and small myelinated fibers. Unmyelinated nerve fiber sprouting was evident. The clinical features, which suggested small-fiber involvement, correlated with the pathological findings in biopsied cutaneous nerve. The balance of evidence indicates that the painful small-fiber neuropathy of diabetes is an axonal disorder.