Paraneoplastic syndromes are disorders associated with cancer but without a direct effect of the tumor mass or its metastases on the nervous system. Small cell carcinoma of lung associated with paraneoplastic sensory neuronopathy and/or paraneoplastic encephalomyelitis with the presence of anti-Hu antibodies has been termed "anti-Hu syndrome." Anti-Hu associated PSN-PEM is an immune disorder in which both cell-mediated and humoral mechanisms are involved. Patients are considered affected by Anti-Hu associated PSN-PEM when they develop clinical signs and symptoms of CNS dysfunction and/or sensory neuropathy not caused by metastases or other disorders, and serum or cerebrospinal fluid is positive for Hu abs. SCLC is found in more than 90% of patients with cancer and positive Hu abs. Individual patients with Hu abs associated to SCLC may suffer PSN-PEM, limbic encephalitis, brainstem encephalopathy, opsoclonus-myoclonus, paraneoplastic cerebellar degeneration or myelopathy. Hu abs have a specificity of 99% and sensitivity of 82% in detecting paraneoplastic neurological syndromes. There are two types of treatment: the first is to treat the cancer, the second is to suppress the immune reaction with the use of corticosteroids, cyclophosphamide, azathioprine, plasma exchange, intravenous immunoglobulin and immunoadsorption; however, treatment of paraneoplastic syndromes is generally unsatisfactory.