The case histories of five children, four boys and one girl (1 to 9 years of age), who developed autistic behavior after the onset of infantile spasms, are presented in detail. The patients' initial EEGs disclosed hypsarrhythmia. First onsets of seizures occurred during the second 6 months of life in four and on the third day of life in the youngest whose diagnosis of autism was tentative. Seizures disappeared in one case, persisted in two despite Rx, and subsided in two receiving Dilantin. The possibility of an association between the two disorders is discussed in light of their unknown etiology.