A 17-year-old epileptic was admitted to the hospital in a confused state. Electroencephalography (EEG) with polygraphic recording revealed tonic status epilepticus. Therapy with phenytoin, phenobarbital, valproic acid, and methylphenidate was unsuccessful. Intravenous diazepam exacerbated the seizures. EEG with polygraphic recording may detect clinically inapparent tonic seizures in epileptics with unexplained confusion, and when generalized paroxysmal fast activity occurs during EEG recording.