Twenty girls were diagnosed as having Rett's Syndrome (RS) based on criteria decided upon in 1988. Fifteen suffered epileptic fits, four of which were possible to record by EEG. In this work we report on the clinical EEG semiology of these girls. All underwent clinical, biochemical, electroneurophysical, neuroimaging and cytogenetic studies. Periodic EEG were carried out while the girls were awake and the recorded fits were so obtained. All had night-time EEG. Four girls had their first fits between 5 years 4 months and 6 years 5 months (average 6 years). The ages at which their attacks were recorded varied from seven to eleven years. Two girls presented tonic-axial attacks expressed graphically by desynchronisation in the EEG in one case and rhythmically in the other, one having had atypical simple absences expressed on EEG as point-wave complexes at a rate of two per second, the other presenting two types of attack: initially tonic-axial fits expressed as a low amplitude rhythm and a year later generalised clonal fits expressed as slow waves with sharp waves in between. Outstanding is the fact that despite the diversity of epileptic fits described in RS all such attacks recorded were of a generalised type.