Despite growing interest in the Landau-Kleffner syndrome there have been few reports dealing with language disorders in recent years. The authors present a clinical case of a child with Landau-Kleffner syndrome focusing particularly on the relationship between language disorders and electroencephalographic abnormalities. The authors emphasize that the language disorders primarily affect the receptive sphere and that there seems to be a relationship between abnormalities during sleep with a deterioration in verbal comprehension.