The syndrome of acquired aphasia, dementia and behavior disorder in a child with partial complex epilepsy and continuous spike and waves during sleep is reported from the Service de Pediatrie, et Service de Neurologie, CHUV, Lausanne, Switzerland. The child was observed from age three to 18 years and deterioration in behavior and language occurred between the ages of 3-1/2 and 5 years, coinciding with the period of maximal EEG activity and the presence of almost continuous spike waves during sleep (CSWS). Improvement coincided with the disappearance of CSWS, between the ages of 5-1/2 and 6-1/2 years, and the onset of a unilateral focus that persisted throughout the following years. A definite correlation between the paroxysmal EEG abnormalities and the neuropsychological deterioration and improvement was established retrospectively. 
COMMENT. Complex partial seizures with recurrence in adolescence and the persistence of an epileptic focus on the EEG are atypical features of the Landau-Kleffner syndrome but this diagnosis could not be definitely excluded.