Summarizing the main contributions which resulted in modern conception the authors point out that hypsarhythmia does not constitute a clinical entity but an electro-clinical syndrome, usually occurring in early childhood, whose diagnosis can only be made on the basis of characteristic electro-encephalographic records. The authors analyse the etiological factors as they generally occur in the infantile encephalopaties and call attention to the etary factor, traumatic conditions, as well as the problem of neonatorum cerebral anoxia. Emphasis is given to the phenomenon of cerebral maturation which explains the peculiar characteristics of the syndrome. Hypsarhythmia may develop in a previously healthy individual or in an encephalopath. Its evolution is variable since it may evolve favorably, a rare occurrence, or may change either to a focal or some other type of epilepsy which is more common, or it may remain unaltered. This evolution - the natural history of hypsarhythmia - is considered specially from the electroencephalographic standpoint, being or not accompanied by the corresponding clinical evolution. The symptomatology is variable, and it should be noted that the spasms in flexion are predominant. The anatomo-pathological data are scarce; the authors only add some details referring to the autopsy of one of their cases, without any specific data. The prognosis, mostly unfavorable, may change specially after the use of ACTH. The treatment is a difficult and frequently disappointing one. The best results are obtained with ACTH and, sometimes, with antibiotics and symptomatic medication but, almost always, when medication is discontinued, the symptomatology recurs. On the other hand, it is not always possible to continue with the medication.