Abstract We studied a patient with polyradiculoneuropathy with anaplastic carcinoma of the thymus. Motor manifestations dominated. Postmortem examinations indicated that the primary changes were in the spinal nerve roots, peripheral nerves and, possibly, the spinal anterior horn cells. The posterior funiculi and posterior root ganglia were also affected, implying multifocal and multiphasic degeneration. This unusual polyradiculoneuropathy is a form of carcinomatous neuropathy.