Sixteen cases of SSPE were diagnosed among ten thousand patients whose EEG was done between August-1966 and February-1972 in the EEG Service of the Institute of Neurosurgery and of the Catholic School of Medicine, Porto Alegre, Brasil. In all cases the diagnosis of SSPE was made by the presence, during long periods of time, of periodic jerks and psychomotor deterioration, associated to periodic complexis in the EEG, and abnormal cerebrospinal fluid. The authors study the evolution of several EEG aspects during the progression of the disease.