AbstractWe evaluated, at our institute, 70 females with Rett syndrome between 2 ½ to 34 ½ years old. This provided an opportunity of observing the natural history of this condition. The evolution of a subacute encephalopathy of very early onset, maximizing in the second year of 1ife, with slow recovery and devastating sequelae, was recognized. The hyperorality, visual auditory and tactile agnosia with aphasia and seizures resembled symptoms described in human Kluver Bucy syndrome. Over interpretation of behavioral abnormalities as seizures was common. Scoliosis was not a necessary concomitant of age. A consistent biochemical or neurophysiological abnormality was not detectable in understanding the cause and pathogenesis of this disease process. Life span appears to be unaffected though life tables have not yet been establishe