Introduction: Paraneoplastic neurological syndromes (PNSs) are mostly associated with non-epithelial ovarian cancers. We report the case of an advanced high-grade serous ovarian adenocarcinoma, diagnosed during the etiological investigation of a subacute motor-sensory axonal neuropathy variant (AMSAN) of Guillain-Barre syndrome (GBS). According to our literature review, only a single case-control study described a positive association between GBS and cancer. Case Report: A 73-year-old woman was admitted to the emergency department for a progressive symmetrical distal tetraparesis, associated with hypoesthesia and abdominal pain. There was no sign of viral or bacterial infection. Over a period of 10 days, she presented a rapid neurological deterioration with nearly complete paralysis of all extremity, facial, and respiratory muscles. The laboratory testing ruled out active infection but the computed tomography (CT) scanner described diffuse peritoneal carcinomatosis, associated with bilateral ovarian tumors. Laparoscopic biopsies confirmed a high-grade serous ovarian cancer. Cerebrospinal fluid analysis confirmed the presence of elevated protein with a normal white blood cell count and anti-ganglioside autoantibodies anti-GD1b and anti-GM1. The patient received systemic chemotherapy together with plasmapheresis and intravenous immunoglobulins, and she experienced a rapid neurological recovery and long-term tumor remission. Conclusion: Neurological paraneoplastic syndromes are rarely associated with epithelial ovarian cancer. Cerebellar ataxia is most frequently associated with this cancer type. Guillain-Barre syndrome can rarely be associated with high-grade serous ovarian cancer. It can delay the tumor diagnosis and treatment. In the case of our patient, early supportive and etiological treatment was of paramount importance for the complete recovery of our patient.