Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular junction disorder characterized by fluctuating proximal limb muscle weakness, decreased deep tendon reflexes and various autonomic symptoms. LEMS is reportedly the most common neurological paraneoplastic syndrome. This is the case report of a patient with small-cell lung cancer (SCLC) who developed LEMS. A 68-year-old male patient presented with a 6-month history of progressive weakness of the proximal limbs and a 2-month history of xerostomia. The patient was admitted to the Department of Neurology of the People's Liberation Army General Hospital of Shenyang Military Region (Shenyang, China). The symptoms of the patient were not relieved with supportive therapy. Further laboratory tests, electrodiagnostic studies, chest computed tomography and immunohistochemical staining confirmed the diagnosis of LEMS in the presence of SCLC. Following administration of two cycles of rescue chemotherapy with a combination of etoposide and cisplatin, the symptoms of the patient were gradually relieved and, after six cycles of therapy, the primary malignancy completely regressed. In conclusion, a diagnosis of LEMS may lead to the timely detection of SCLC, significantly improving patient prognosis and survival.