Paraneoplastic neurological syndromes (PNS) are infrequent tumor-related disorders that are not caused by direct tumor invasion or metastases, metabolic and nutritional deficits, infections, coagulopathy, or the side effects of cancer treatment. PNS can affect any part of the central and peripheral nervous systems, the neuromuscular junction, or muscles. Because the onset of PNS often antedates the diagnosis of an underlying cancer, it is difficult to establish a definitive early diagnosis. Therefore, it is important for neurologists to consider the possibility of PNS when rapidly progressive neurological syndromes cannot be explained by other causes. Detection of onconeural antibodies is useful for diagnosing PNS, and detection of specific antibodies can aid the identification of the underlying tumor. However, not all patients with PNS have onconeural antibodies, and not all patients with onconeural antibodies have PNS. Although PNS are considered to be mediated by the immune system, various forms of immunotherapy have yielded disappointing results, with some exceptions (i.e., PNS cases with antibodies against neuronal cell-surface antigens such as N-methyl-D-aspartate receptors). The lack of clinical trials due to the rarity of patients with PNS makes it difficult to test the efficacy of immunomodulatory treatment. Rapid detection and immediate treatment of the underlying tumor is an important approach that offers the highest chances of improvilng or stabilizing the syndrome before irreversible neuronal damage occurs. In this review, we discuss the diagnostic criteria and management of PNS based on the PNS Euronetwork and other reports.