Morphometric evaluations of histopathological changes in postmortem materials from three patients with diabetes mellitus with neuropathy, nephropathy, and retinopathy were made on the sural nerve, lumbar spinal roots, lumbar dorsal root ganglion (2 cases), and fasciculus gracilis. In all three patients there was a marked decrease in densities of both the large and the small myelinated fibers in the sural nerves. In the lumbar spinal roots, segmental demyelination and remyelination with or without decrease in the number of myelinated fibers per root was the main finding in both dorsal and ventral roots, being more common in the dorsal roots. At the third cervical segment of the fasciculus gracilis, the myelinated fiber density was slightly decreased in one patient and moderately decreased in the other two. The number of cell bodies of the fifth dorsal root ganglion was within normal limits in the two patients where this was examined, although the median diameters approximated the lower limit found in controls. The potential presence of segmental demyelination and remyelination in dorsal and ventral spinal roots should be considered especially when assessing electromyographic changes and nerve conduction in diabetic patients.