Paraneoplasic neurological syndromes are defined as an association between neurological disease and cancer in the absence of metastatic, infectious or metabolic complications. These syndromes occur in less than 1% of patients with cancer. With the exception of the Lambert-Eaton syndrome in which an autoimmune mechanism has been proven, the pathogenesis of paraneoplasic neurological syndromes remains unknown despite a frequent association with anti-Hu, anti-Yo, and anti-Ri antibodies. Neither passive transfer of these antibodies nor immunization with recombinant proteins has been able to produce paraneoplasic syndromes in animal models. It is most likely that cell immunity or other antigenic mechanisms are also implicated and that the synthesis of anti-Hu, anti-Yo or anti-Ri is simply one manifestation of a more complex immune reaction. Nevertheless, the discovery of these antibodies can be useful in the diagnosis of cancer, especially in the early stages. Other antibodies, specific for paraneoplasic neurological syndromes, will undoubtedly be discovered in the future, increasing the capacity of immunological diagnosis. A better understanding of immune cross reactions between the tumor and the nervous system may help further our understanding of the immune system and lead to progress in specific treatment for paraneoplasic neurological syndromes.