SummaryThis is a case of pinealomatous teratoma found in 22 years‐old male with diabetes insipidus as an initial symptom and complicated of late by development of the anterior pituitary insufficiency. Despite lack of increase of intracranial pressure until one month prior to death, postmortem examination revealed occurrence of a tumor occupying almost all the diencephalic regions and the central gray of the mid‐brain, leading to obliteration of the aqueduct ofSylvius. The relationship between the peculiar pupillary reflex and the damage in the nuclei of the central nervous system was studied, together with consideration of the cause of lack of intracranial hypertension. Conclusion maintains that hypernatremia and hyperchloremia were caused not only through dehydration process but also through disturbance of sodium and chloride regulation cen