The authors encountered an interesting case who had had the periodic attacks of twilight state, with accompaniment of marked autonomic deficiencies (flushing of the face, sweating, polydipsia, abdominal pains, pollakiuria, polyuria, and insomnia), 10 times since the age of twelve. Somatically and neurologically, no striking changes other than vagotonia and adrenalinresponse blood-sugar curve belonging to what Kato et al. call First Curve Group B type, have been observed; yet by dividing the duration of periodic attacks into five phases and studying the progress and the genetic factors of this disease both from the psychiatric and the somatic standpoints, it leads to the conclusion that the case might possibly be included in the diencephalic syndrome. Chlorpromazine therapy offers markedly beneficial effects on this case as shown by the disapperarance of twilight state and the stabilization of autonomic deficiencies. And since the decrease in the amount of urine and the rate of its stabilization parallel with the amounts of chlorpromazine administered, it can be assumed that this drug is quite efficacious to diabetes insipidus.