The authors are members of the Department of Paediatrics and Child Health, University of Birmingham, and their patients were studied at All Saints and The Children's Hospitals, Birmingham, England. The literature is reviewed in part I, and the results of a study of 112 patients examined between 1954 and 1963 are described in part II. Despite the fact that most of the findings have been mentioned in the literature and a few important references have been overlooked, this monograph is a useful addition to the recent spate of publications concerning infantile spasms and hypsarhythmia. The authors reemphasize that hypsarhythmia is a laboratory finding and not a diagnosis. The clinical triad of infantile spasms, hypsarhythmia, and mental retardation is a symptom complex associated with diverse factors of presumed etiologic importance in approximately one half of the cases and of undetermined cause in the remainder.