The multifocal motor neuropathy is an immunological disease that courses with an asymmetrical distal weakness, usually predominant in the upper limbs.It is not rarely misdiagnosed as a motoneurone disease because of the frequent occurrence of fasciculations and cramps and the absence of sensory symptoms. Neurophysiological studies are essential for the proper diagnosis, disclosing the presence of conspicuous alterations of the nerve conduction that are mainly of demyelinating type and occur exclusively in the motor fibers. The nerve conduction blocks characteristically found in this disease are long lasting, multifocal but preferentially proximal, and they are out of the typical levels of the compression neuropathies. High titers of IgM antibodies, mainly anti-GM1, are frequently observed although their pathogenetic significance has not still been completely established. In many cases, even in those with very prolonged evolutions, treatment with high doses of parenteral immunoglobulins has been effective.