Abstract
One hundred and five children who had shown the electroencephalographic (E.E.G.) features of hypsarrhythmia in the first year of life (1956-62) were assessed in 1969 in respect of death and mental development. Irrespective of the presenting symptomatology, and to some extent irrespective of therapy, mortality in the group was of the order of one in four (mostly before the age of 3 years) and the incidence of mental subnormality in the survivors was 77%. Only 18 children attained fairly normal standards of mental development and could attend ordinary schools. It seems that whatever the clinical picture at the time, the presence of hypsarrhythmia in the E.E.G. of an infant is a physical sign of grave prognostic implications.