ABSTRACT.The Rett syndrome is presumed to be a neurodegenerative disorder of childhood and adolescence occurring solely in girls. The EEG is almost invariably abnormal and frequently demonstrates prominent paroxysmal discharges. This finding corresponds with frequent occurrence of epileptic seizures. Spike activity is quite often accentuated over the central region and may be attenuated or blocked with passive hand movements. Slow spike-waves may also occur. Starting with the end of the first decade, the Rett syndrome tends to lose its progression and comes to a standstill. Epileptic seizures tend to abate while residual neurological damage (along with EEG slowing) persists. Sleep recordings also show unusual features with decline of physiological patterns and burst-like anterior delta waves.