Since the first cases described in 1986, multifocal motor neuropathy with persistent conduction blocks (MMN) appears to be a well-defined nosological entity. Clinical features include male-predominant occurrence, weakness often accompanied by cramps and fasciculations; topography of the motor involvement is characterized by assymetry, upper limb predominance, relation to the distribution of individual nerves or roots. Atrophy is variable but can lack despite severe weakness. Multifocal, purely motor and persistent conduction blocks are the electrophysiological hallmark of the disease. Serum antibodies against ganglioside GM1 are frequently associated with MMN but their diagnostic sensitibity and specificity are discussed. However high level of these antibodies may be a useful immunological marker of MMN. Their pathogenic role is probable, perhaps by their interaction with ionic channels localized in node of Ranvier. Morphological findings, immunologic abnormalities and improvement with intravenous immunoglobulin therapy define MMN as a type of inflammatory demyelinating neuropathy. Their relation with CIDP are discussed.