Paraneoplastic neurological syndrome is an autoimmune disease caused by distant effect of tumor. Lambert-Eaton myasthenic syndrome (LEMS) is a paraneoplastic disease that is associated with voltage-dependent calcium channel antibodies. These autoantibodies affect especially presynaptic neuromuscular area. A 65-year-old male patient admitted to hospital with complaint of dizziness, walking difficulty, and difficulty in getting up stairs. Neur ological examination showed mild muscle weakness proximal of lower extremities. Deep tendon reflexes were hypoactive. Sensory nerve conduction was normal in the electroneuromyography. All motor nerve compound muscle action potential (CMAP) amplitudes were decreased. After 10 seconds of exercise, amplitude increased more than 100%. More than 10% decrement was observed at low frequencies in ulnar repetitive nerve stimulation. More than 200% increment was observed with 50 Hz tetanic stimulation. Lung adenocarcinoma was diagnosed with thorax computerized tomography and bronchoscopic biopsy. In the electrophysiological analyses of LEMS, significant amplitude increment is diagnostic with high frequency tetanic stimulation. Increment following short-term exercise is an easier alternative method to tetanic stimulation.