The paraneoplastic neurological syndromes are alterations associated with neoplasias. However, they are not caused by metastases or complications such as infections, vascular disorders, metabolic or nutritional alterations or secondary effect of treatment. The paraneoplastic syndromes are often associated with the creation of autoantibodies against antigens produced by the neoplastia, but also may be against other cells or target molecules of the patient. Sometimes, especially with antibodies directed against cell membrane proteins, there is a close relationship between the antibody and the target organ, as for example antibodies against the acetylcholine receptor in myasthenia gravis. On other occasions, especially when the antigen is intracellular, the mechanism of the autoantibody reaction is not known. Finally, in a third group, the antibody associated with a particular paraneoplastic neurological alteration has not been identified. In this paper we describe the main paraneoplastic neurological pictures and known antibodies, including the molecular aspects and the neoplasias most frequently related to them.