To our knowledge, this is the first reported application of immunoadsorption in a patient with multifocal motor neuropathy (MMN). The diagnosis relied on the typical clinical features, markedly increased IgM-GM1 antibodies, multiple motor conduction blocks, and motor nerve biopsy. Immunoadsorption was carried out in seven cycles of two sessions each within 97 days. From the first therapy, muscle force as well as nerve conduction velocity and conduction blocks deteriorated continuously. As a consequence, immunoadsorption cannot be recommended as a treatment for MMN.