BACKGROUND: Tetanus toxin selectively blocks inhibitory synapses in the brainstem as well as the spinal cord. Therefore, in contradiction to Stiff Person syndrome, patients with generalized tetanus usually show abnormal masseter silent periods as well as abnormal F/M amplitude or H/M amplitude ratios. This study aimed to verify the characteristics of electrophysiological findings of generalized tetanus. METHODS: The authors retrospectively studied clinical and electrophysiological characteristics of 7 patients with generalized tetanus, who were admitted to the neurology department of Hallym Medical Center from 1995 to 2005. RESULTS: All the seven patients showed abnormal masseter silent periods. Three of them showed somewhat improvement in the silent period at follow-up study as trismus was improving. Full NCSs done in two patients did not show any abnormalities except an increased F/M amplitude ratio. One patient with a wound site in his left finger showed an abnormal F/M amplitude ratio only in the right upper extremity without involvement of other extremities. Another patient showed an increased H/M amplitude ratio without an increased F/M amplitude ratio. (In this patient we did not conduct full NCS tests.) CONCLUSIONS: The Masseter silent period could be used as a diagnostic tool and parameter of clinical improvement in patients with generalized tetanus.