Motor neuropathy with multifocal conduction blocks represents a recently identified autoimmune disorder of the peripheral nerve myelin. Association of motor neuropathies or neuronopathies with thyroid disorders, such as hyperthyroidism, hypothyroidism or thyroid neoplasms has been rarely described. We studied a 61-year-old man with a 2-year-history of slowly progressive weakness of the left limbs with atrophy and fasciculations. Nerve conduction velocity studies revealed multifocal motor conduction blocks. Serum IgM titer of antibodies against GM1 was elevated (1:1280; n.v. up to 1:640). Thyroid studies were compatible with Hashimoto's thyroiditis. Therapy with high dose intravenous immunoglobulins was followed by a prompt clinical recovery. Then the disease assumed an intravenous immunoglobulins dependent course with a full clinical, but transient, recovery. This is the first observation of an association of multifocal motor neuropathy with high titers of GM1 and Hashimoto's thyroiditis and reinforces the multifocal motor neuropathy autoimmune origin as well as the repeated clinical recoveries after intravenous immunoglobulins. This case also suggests to deeply investigate the thyroid function in patients with multifocal motor neuropathy.