A 28 year-old man who had been diagnosed as having Dravet syndrome (DS) since his childhood by a pediatric hospital was referred to our department from the local pediatric clinic. Until then, his seizures were medically intractable, and generalized tonic-clonic convulsions had occurred monthly even when administered enough valproate, zonisamide and clorazepate. After adding levetiracetam (LEV) to his drug regimen at the age of 29, the seizures disappeared for more than one year. LEV was found to be effective in this adult patient as well as in a series of children affected with DS.