A 67-year-old man was admitted due to weakness, coughing, shortness of breath and fever. He had decreased breath sounds in the left lung and muscle weakness in the lower and upper extremities. Chest imaging showed a mass in the left lung, and a biopsy revealed small cell lung cancer. The nerve conduction velocity was decreased, and anti-GM1 IgG antibodies were positive. The patient showed a temporary neurologic recovery following the administration of cancer chemotherapy, although he eventually died of progression of lung cancer. As a result of the almost simultaneous symptomatic development of lung cancer and Guillain-Barré syndrome, this case may be considered to involve a paraneoplastic neurologic syndrome.