Neurological manifestations are uncommon in myeloma patients, and subacute polyradiculoneuropathy as the inaugural manifestations of solitary plasmacytoma of bone is exceedingly rare. We report the case of a 52-year-old man who was evaluated for a three-month history of flaccid tetraplegia with a gradually ascending onset and for a deterioration in general health. Electromyography findings were consistent with polyradiculoneuropathy. Laboratory tests showed a moderate amount of a monoclonal IgG-lambda antibody. Findings were normal from a radiographic bone survey and a radionuclide bone scan. Computed tomography of the pelvis disclosed a solitary osteolytic lesion in the right iliac crest, which was found upon biopsy to be a malignant plasmacytoma. Radiation therapy and chemotherapy were given. Subacute or chronic polyradiculoneuropathy as the inaugural manifestation of solitary plasmacytoma is exceedingly rare and should be distinguished from the sensorimotor polyneuropathy produced by plasma cell infiltration in some multiple myeloma patients. The polyradiculoneuropathy of solitary plasmacytoma can be likened to the neuropathies seen in some forms of multiple myeloma (sclerotic myeloma and POEMS syndrome). The pathophysiology of these neuropathies remains obscure. The case reported here suggests that patients with unexplained lasting polyradiculoneuropathy should be investigated for a plasma cell proliferation even if they have no serum monoclonal component. Because plasmacytomas are painless, imaging studies are needed for their diagnosis. The management of the neuropathy consists in treatment of the tumor.