In a consecutive series of 30 patients with chronic inflammatory demyelinating polyneuropathy (CIDP) minor clinical evidence of CNS involvement was found in five. Cranial magnetic resonance imaging (MRI) was performed in 28 and revealed abnormalities consistent with demyelination in nine patients aged less than 50 years and abnormalities in five aged 50 years or over. Measurements of central motor conduction time (CMCT) were obtained in 18 and showed unilateral or bilateral abnormalities in six. It is concluded that subclinical evidence of central nervous system (CNS) involvement is common, at least in patients with CIDP in the United Kingdom, but that clinically evident signs of CNS disease are infrequent. The association of a multiple sclerosis-like syndrome with CIDP is rare.