extracted from the Statistical Review for England and Wales, 1968 (Registrar General, 1970): the mortality in children between 1 month and 5 years of age is about 1 : 1,000 while in our group of children who had a hypsarrhythmic E.E.G. the figure is about 1 : 4.According to educational psychologists, an accepted figure for children of school age with an I.Q. above 70 is about 97%, while in our series only 23% of the surviving patients achieved this level. If we then consider 30/ as an accepted figure for mentally subnormal children in the general population, the figure in our series is of the order of 770%. These findings therefore suggest that the presence of a hypsarrhythmic E.E.G. in the first year of life, irrespective of the clinical symptomatology at the time and largely irrespective of therapy, carries grave prognostic implications in terms of incidence of mental subnormality and early death. Since not all infants with a severe neurological illness in the first year of life develop hypsarrhythmia in their E.E.G., it is tempting to suggest that the presence of hypsarrhythmia might indicate a special type, or group, of disorders as yet unidentified.