BACKGROUND: It has been known for decades that monoclonal IgM gammopathies are associated with peripheral neuropathies. However, available data are from ultraspecialized laboratories, while little is reported about their epidemiology. PATIENTS AND mETHODS: Since 1988 we have recorded a registry of the patients referred for a peripheral neuropathy. Database included clinical, electrophysiological, laboratory, immunological and pathological data. All the patients were followed‐up with clinical visits or at least phone interview every six months. In case of death we evaluated death certificates and contacted general practitioners. Results: In the period from 1988–1999 we saw and followed‐up 512 patients with clinical ascertained peripheral neuropathy. Of those patients, 35 (6.8%) had a MGUS: 18 IgG, 10 IgM, and 7 IgA. The patients with IgM paraprotein were all men, except 1 woman, aged 48 to 71 years at the onset of symptoms. Eight patients had a predominantly sensitive neuropathy and two patients a motor neuropathy. Of the 8 patients with sensitive neuropathy, 3 had a demyelinating disease and antiMAG antibodies, 4 an axonal disease and antisulphatide antibodies, and 1 an axonal neuropathy with both antiMAG and antisulphatide antibodies. The two patients with motor neuropathy had both an axonal disease and anti‐GM1 antibodies. The patients with sensory neuropathy were treated with periodic plasmaphoresis plus i.v. cyclophosphamide every 4–6 months. The patients with motor neuropathy were treated every month with i.v. immunoglobulins alternated with i.v. cyclophosphamide. Follow‐up of those patients lasted 12 to 108 months. Four patients died: 3 with antisulfatide antibodies because of a developing cancer (2 a primary hepatic cancer and 1 a bladder neoplasm) and 1 with anti‐GM1 antibodies for respiratory failure. The remaining patients showed a slowly progressive invalidating disease especially with the loss of hand ability. Conclusions: The patients with monoclonal IgM gammopathy are a minority among those observed because of a peripheral neuropathy in a General Hospital. Prognosis is severe either because of growing dependency or of life shortening (directly or for developing cancer). Aggressive therapies probably deserve multicentric studies.