Abstract Background. PET/CT may be particularly useful to detect the primary cancer in paraneoplastic cerebellar degeneration (PCD) with anti-Yo which is most commonly associated with breast, ovarian and other gynecological cancers. Case. A 60-year-old woman developed a PCD associated with anti-Yo antibodies in serum and cerebrospinal fluid. Conventional imaging was negative. FDG-PET showed an abnormal hot spot in the right ovarian area associated with lombo aortic lymph nodes. The diagnosis was confirmed by surgery as an ovarian adenocarcinoma. Conclusion. In this case report, FDG-PET played a crucial role in detecting the unknown primary tumor in a patient with PCD.