Two patients with brachial plexus neuropathy had recurrent symptoms for years that culminated in the development of a painful lower cervical mass. On macroscopic examination the affected nerves had a fusiform segmental enlargement, suggestive of a nerve sheath tumor, that was excised. Histologically, marked endoneurial edema, florid focal chronic inflammation, extensive onion bulb formation, and perineurial sparing were seen. Electron microscopic studies on one patient revealed microvasculitis; frequent tubuloreticular inclusions in endothelial cells, histiocytes, and lymphocytes; and cylindrical confronting cisternae in lymphocytes. We conclude that some cases of recurrent brachial plexus neuropathy are due to a localized chronic inflammation that may be related to autoimmunity or to a viral infection.