In order to study whether axonal polyneuropathy associated with monoclonal gammopathy of undetermined significance (MGUS) is a distinct entity, we prospectively studied the clinical, electrophysiological and pathological features of 16 patients with chronic idiopathic axonal polyneuropathy (CIAP) with MGUS (CIAP-MGUS) and compared them with those of 71 patients who had CIAP without MGUS. In patients with CIAP-MGUS the arms were more frequently affected and the disability was worse. On electromyography there was more evidence of denervation in patients with CIAP-MGUS. All other clinical symptoms, signs, nerve conduction parameters and nerve biopsy findings, showed no differences between both groups. Antibodies against myelin associated glycoprotein (MAG), GMI-ganglioside and chondrotoin sulphate were not present. Only one patient with an immunoglobulin M (IgM)-MGUS and a sensory neuropathy had antibodies against sulphatide. In conclusion, axonal polyneuropathy in patients with and without MGUS are essentially indistinguishable rather than different, suggesting that the MGUS may be coincidental in most patients.