Introduction: Paraneoplastic Cerebellar Degeneration (PCD) is a rare paraneoplastic syndrome, and difficult to diagnose. PCD is associated with certain types of cancer such as ovarian cancer, uterus or its annexes, breast cancer, Hodgkin's lymphoma and small cell lung cancer (SCLC), however, this syndrome is not associated with metastatic dissemination. Here we report a case of a patient with advanced SCLC, which develop PCD. Case Report: Female patient, 51-year-old, large smoker, with advanced SCLC with involvement of abdominal lymph nodes, presented muscle weakness, without spinal cord level, during second-line treatment with Cisplatin and Irinotecan, even with important clinical response to chemotherapy. The patient developed nystagmus and cerebellar ataxia. Cerebrospinal fluid analysis and brain magnetic resonance imaging without findings. The patient was assessed by neurologist, with clinical diagnosis of subacute PCD. Patient started pulse therapy with methylprednisolone, with significant remission of neurological symptoms. Discussion and conclusion: PCD finding, although rare, usually precedes the detection of a tumor, and it is important to start early research and treatment of cancer because of better survival and patient´s quality of life. This case differs from usual descriptions found in the literature because the patient developed PCD during good clinical response in second-line treatment. PCD evolves with progression of the neurological condition in weeks to months and then stabilizes. The low incidence difficult to establish treatment strategies based on evidence for PCD, usually taking up aggressive immunotherapy, using intravenous immunoglobulin, plasmapheresis, steroids at high doses and/or immunosuppressive drugs.