This is the case report of a 61-year-old woman who presented with progressive diplopia and ataxia. Her cerebrospinal fluid revealed high titers of anti-Yo (PCA-1) antibody and a magnetic resonance imaging with contrast showed cerebellar degeneration. Extensive imaging workup was negative for malignancy and she was otherwise asymptomatic. Given the association between anti-Yo antibodies and gynecologic malignancies, she underwent a bilateral salpingo-oophorectomy and cancer staging. Extensive section of the fimbriated end of the fallopian tube revealed a stage 1, microscopic serous adenocarcinoma. After surgery, her anti-YO titers fell and plans were made for adjuvant chemotherapy. Her neurologic symptoms are not expected to substantially improve, illustrating the urgent need for early surgical investigation in cases of paraneoplastic syndrome, even in the absence of imaging evidence of a lesion.