The pathogenesis of the rare hypernatremia, usually described in the literature as "neurogenic" or "essential" hypernatremia, consists of defective thirst mechanism either alone or in combination with impaired osmoregulation of ADH release. As etiology, disturbances of the neoplastic, vascular and degenerative type and malformations in the hypothalamic area are known. In patients with the hypodipsia-hypernatremia syndrome, dysfunction of the anterior pituitary lobe, obesity, abnormal regulation of body temperature, psychomotor retardation and episodic muscular weakness are frequently encountered as additional abnormalities. A 6-year-old patient is described with hypodipsia-hypernatremia syndrome manifest for 3 years. Besides hypernatremia, hypodipsia and the relative insensitivity of the osmoreceptors regulating ADH release, elevated body temperature, polyphagia and obesity, partial hypothalamic-hypophyseal dysfunction, lethargy and psychomotor retardation are the principal findings. An inflammatory lesion or one occupying an intracranial space was not demonstrable until now. Under forced water intake and hypocaloric diet the patient has progressed well with nearly complete normalization of the hypernatremia, body temperature and obesity.