Severe persistent neuropsychological disorders sometimes develop in the course of a focal epilepsy of unknown origin in previously normal children. Very frequent bilateral focal or generalized discharges are often noted on the sleep EEG records of these patients with no evidence of clinical seizures. The relation between these paroxysms and the observed deterioration remains unclear. We report a child with a partial complex epilepsy and severe disturbances of language, cognition, and behavior acquired in the early years of development who was followed for 15 years. A correlation between the evolution of the striking EEG abnormalities during sleep and the neuropsychological disorders could be established retrospectively. The observed sequence of onset and recovery of the aphasia, the dementia, and the "psychotic" behavior makes a direct causal relation between the deficits quite unlikely. Rather it suggests an association of independent symptoms with a specific language disorder becoming manifest in the course of the evolution. This child shows many of the main characteristics of the syndromes of "acquired aphasia with convulsive disorder" (Landau-Kleffner syndrome) and "epilepsy with continuous spike waves during sleep." Both syndromes describe probably different facets of a similar underlying, still unexplained cerebral dysfunction.