Clinical and electroensephalographic aspects of twenty seven (27) patients with Lennox-Gastaut syndrome were studied (20 without previous West syndrome, group A, and 7 with this antecedent, group B). The epileptic seizures were characterized through descriptions made by relatives who were in close contact with the patients, and also by direct observation by the author in the clinic. The direct observation was possible due to high frequency of the seizures. Denominations were given to the manifestations not previously mentioned in the literature, according to the quality and eventual sequence of observable phenomena, in agreement with the terminology used by the Clinical and EEG Classification of Epileptic Seizures. The incidence, prognostic, clinical and evolutive aspects of elementary forms of epileptic seizures were discussed. Great variability of the convulsive seizures was verified, permiting their division into simple, complex and mixed forms.