Paraneoplastic neurological syndromes consist of a dysfunction of any part of the nervous system, in isolation or in combination, caused by a malign neoplasia, but not by the direct tissular or metastasic invasion of the tumour. Their pathogeny is explained by immunological mechanisms and they are characterised by the presence of high rates of antibodies in serum and cerebrospinal fluid. We present the case of a patient with a sensitive neuropathy that produced ataxia, and who suffered from a poorly differentiated adenocarcinoma of the lung, in whom the search for antineuronal antibodies was positive for antiamphiphysin antibodies, supporting the diagnosis of paraneoplastic polyneuropathy.