Paraneoplastic peripheral neuropathies are not common. They are out-numbered by the far more common peripheral neuropathies that occur either as a direct result of the cancer (metastases) or its treatment (usually chemotherapy). Nevertheless, paraneoplastic peripheral neuropathies are important because they may be the first sign of an otherwise occult cancer and/or because they may substantially disable the patient even when the cancer itself is asymptomatic. Paraneoplastic disorders are sometimes marked by the presence of autoantibodies that react with proteins both in the underlying cancer and in the nervous system. Their discovery may lead to an early diagnosis and potential cure of the underlying cancer.