Three different microanalytical methods were used to identify calcium deposits in the sciatic nerve perineurium of a 33-year-old woman who died after developing nephropathy, retinopathy, and neuropathy as complications of diabetes. Scanning electron microscopic x-ray microanalysis (SEM-XMA) enabled localization of calcium and phosphorus elements to the perineurium in whole nerve cross sections. With SEM-XMA and scanning-transmission electron microscopic x-ray microanalysis (STEM-XMA) of the minute crystallites in the perineurium, the approximate relative amounts of calcium and phosphorus in the deposits were found to correspond to those in calcium hydroxyapatite. Finally, the crystallites were specifically identified by selected area electron diffraction, and were found to be composed mainly of calcium hydroxyapatite.