Untreated and rapid correction of neonatal hypernatremia leads to severe neurological complications. We describe the case of a six-week-old female who presented with failure to thrive, and further workup revealed hypernatremic dehydration. Initially, she did not respond to treatment to correct the hyperosmotic state. Treatment with desmopressin was then initiated to determine the cause of hypernatremia. Central diabetes insipidus was confirmed as the patient responded to desmopressin. Serum sodium levels then dropped significantly, and the patient had three seizures within 24 hours. Cerebral edema was ruled out through computed tomography (CT) and electroencephalogram. Following the diagnosis of central diabetes insipidus, anterior pituitary hormone levels were obtained and found to be decreased. An investigation into the possible cause of panhypopituitarism led to the final diagnosis of septo-optic dysplasia, including absent septum pellucidum, optic nerve hypoplasia, and panhypopituitarism.