The clinical and laboratory data of a 5-year-old boy with the syndrome of essential hypernatremia are presented. In a four-year follow-up, no demonstrable hypothalamic structural lesion has been identified. Review of the literature has uncovered four similar cases, suggesting a distinct syndrome of altered hypothalamic function. The syndrome is characterized by: adipsia-hypodipsia (5/5 patients), recurrent hypernatremia (5/5), obesity (4/5), inability to excrete a water load (5/5), lack of growth hormone release in response to provocative stimuli (4/4), blunted thyrotropin releasing hormone responses (3/4), hypothyroidism (2/4), and hyperlipemia associated with hypernatremic crisis (1/1). In one of the patients the syndrome has been attributed to a disturbance of the opioid-peptide system.