Multifocal motor neuropathy (MMN) is a purely motor multineuropathy characterized by multifocal conduction blocks on motor nerves. The pathogenesis of MMN is not known but its frequent association with anti-ganglioside antibodies and the improvement after immune therapies support an immune pathogenesis. Patients with MMN do not respond to steroids or plasma exchange, which may occasionally even worsen the symptoms, while the efficacy of other immune suppressive therapies is controversial. More than 80% of MMN patients rapidly and consistently improve with highdose intravenous immunoglobulin (IVIg), the efficacy of which has been confirmed in four controlled studies. In most patients, however, the effects of this therapy only last a few weeks and improvement has to be maintained with periodic infusions for long periods of time, if not indefinitely.