The acquired epileptiform aphasias, with Landau-Kleffner's syndrome as the example, represent an important group of syndromes in our quest to understand the relationship between epilepsy, language, and behavior. The controversy that truly frames the literature on the acquired epileptiform aphasias is the role of epileptiform activity on language, behavior, and cognition. This review expands the model of Landau-Kleffner's syndrome to include two other encephalopathies with language and behavioral regression in association with an epileptiform electroencephalogram. Both of these encephalopathies, autistic epileptiform regression and disintegrative epileptiform regression, are associated with an acquired language disorder. The developmental period in which the acquired language disorder begins, the type of language disorder, and the location and type of the epileptiform activity are all important variables that may affect clinical manifestations and prognosis.