A 67-year-old man was admitted to our clinic because of cough and syncope, and chest X-ray revealed an abnormal shadow. Contrast-enhanced chest computed tomography scan revealed a nodular shadow in the right upper lobe and mediastinal and hilar lymph node enlargement. After a mediastinal lymph node biopsy was performed, he was diagnosed as having small cell lung cancer. Orthostatic hypotension was confirmed in a head-up tilt test, but none of the various tests determined the cause. We suspected that it was associated with lung cancer, which happened to be found at the same time with syncope. Onconeural antibodies were confirmed in the serum, and the cause of orthostatic hypotension was diagnosed as an autonomic symptom due to paraneoplastic neurological syndrome. Autonomic neuropathy due to paraneoplastic neurological syndrome typically presents with multiple symptoms, but can also present with orthostatic hypotension alone.