Hyponatremia caused by a reset osmostat in a neonate with cleft lip and palate and panhypopituitarism.

A neonate with cleft lip and palate and hypopituitarism had persistent hyponatremia despite treatment with hydrocortisone, L-thyroxine, and growth hormone. Serum sodium concentration and urinary osmolality increased and decreased appropriately and concurrently with alterations in sodium and water intake. The ability to regulate serum concentrations of antidiuretic hormone at subnormal serum sodium concentrations indicated a reset osmostat.