The Lambert-Eaton myasthenic syndrome (LEMS) is a rare disorder of neuromuscular transmission that is frequently associated with malignancy, particulary small cell carcinoma of the lung. To our knowledge, there was no report of LEMS in Korean listeratures and this might be the first case in this country. The patient is a 55 year old man with muscle weakness and fatigability of proximal lower limbs for 2 months. Bronchogenic carcinoma is confirmed radiologically and pathologically. The electrophysiological studies suppert the clinical diagnosis of LEMS with (1) low amplitude of evoked compound muscle potential to a single supramaximal stimulus on nerve, (2) significant decremental response at low rates of stimulation and (3) marked incremental response at high rates of stimulation.