Peripheral neuropathy commonly occurs in patients with chronic obstructive lung disease (COPD). We report the presence of peripheral neuropathy in 19 of our 30 COPD patients (63.3%): 7 patients had clinical signs of a symmetric motor and sensory polyneuropathy, 12 patients had only subclinical evidence of peripheral nervous system involvement. Neurophysiological studies showed low amplitude compound muscle action potentials (CMAP) and sensory action potentials (SAP) with only slight reduction of nerve conduction velocity in affected patients: these data confirm an axonal polyneuropathy. The severity of the peripheral nervous system involvement in COPD patients was correlated with hypercapnia, the degree of disability and thus with the severity of COPD. Hypoxia, age and duration of the disease were not related with the presence of polyneuropathy. Improvement of respiratory function produced slight but progressive improvement of neurological symptoms. Within one year, also neurophysiological studies revealed a progressive and statistically significant improvement in CMAP and SAP amplitude and motor and sensory conduction velocity and, in some cases, normal electromyography.