Disturbancies in neurological functions associated with paraproteinaemic states are well documented. In recent years increasing attention has been given to paraproteinemia in the absence of evidence of malignancy. In this article we review the main clinical and pathological features associated with IgM paraproteins. Neurological complications affecting the central nervous system are rare, while peripheral neuropathies are frequently observed. Recent advances at the histological and molecular level have allowed a better characterization of clinical syndromes and have given new insights into their pathogenesis. The most convincing evidence for a causal relationship can be drawn from IgM monoclonal gammopathies with specificities directed against carbohydrate determinants of the myelin associated glycoprotein (MAG). There remain, however, many unresolved questions such as how monoclonal anti-MAG IgM antibodies cross the blood-nerve barrier and trigger a chronic demyelinating polyneuropathy while the central nervous system is essentially spared. Current immune therapies for neuropathy associated with IgM paraproteins are temporarily effective in half of patients and are often associated with considerable side effects which limit their prolonged use and efficacy. The availability of safer therapies such as humanized monoclonal antibodies that eliminate specifically B-cell and B-cell precursors may open a new avenue for the management of these patients.