We report a child with diabetes insipidus and hypodipsia associated with holoprosencephaly. A two-year-old girl with the history of several admittances to hospital during and after the newborn period with hypernatremic dehydration, acute renal failure and convulsions is presented. The patient had hypodipsia, hypernatremia, microcephaly, failure to thrive, and unilateral cleft lip and palate. Magnetic resonance imaging revealed lobar type holoprosencephaly. Increased plasma osmolality and decreased urinary osmolality were detected. Her urine ADH level was 10 ng/day. Plasma osmolality levels returned to normal after hydration and administration of a vasopressin analogue. These findings suggest that in children with hypernatremia-hypodipsia syndrome, the possibility of cerebral malformations should always be kept in mind.