We report 13 patients with pathologically confirmed perineuritis. Seven patients had diabetes mellitus, 5 had nutritional abnormalities, 2 had associated rheumatological illnesses, 2 had sepsis with multiorgan failure, and 1 had a history of malignancy. Electrophysiologic testing demonstrated mononeuritis multiplex in 7, demyelinating neuropathy in 4, distal sensory and motor neuropathy in 1, and polyradiculoneuropathy in 1. Twelve patients received immunomodulating therapy with variable responses. We conclude that perineuritis is associated with a number of different systemic conditions and several clinical patterns of peripheral neuropathy. Response to immunomodulation is variable. The most frequent association is with diabetes mellitus, a previously unrecognized association.