The Lambert-Eaton myasthenic syndrome(LEMS) is a rare disorder of neuro-muscular transmission that is frequently associated with malignancy, particulary small cell carcinoma of the lung. We report a case of 66 year old man who complained of muscle weakness and fatigability of proximal lower limbs on the tappering af prednisolone administeredfor usual interstitial pneumonitis. He was diagnosed LEMS by electrophysiological studies and small cell lung carcinoma by cytologic examination of brochoscopicwashing. The electrophysiological studies support the clinical diagnosis of LEMS with ¨c low amplitude of evoked compound muscle potential to a single supra-maximal stimulus an nerve, ¨e significant decremental response at low rates of stimulation and ¨e marked incremental response at high rates of stimulation.