Osmotic demyelination syndrome (ODS) is a well-known disorder caused by rapid correction of serum sodium. Many conditions including hormonal abnormality are associated with this syndrome. The authors describe two cases of preoperative sellar region tumor associated with hypopituitarism and secondary adrenal insufficiency. These two patients had hyponatremia. Neurological manifestations in both of them were generalized dystonia. Magnetic resonance imaging (MRI) revealed a characteristic extrapontine myelinolysis (EPM). The first case was a 35-year-old man with craniopharyngioma who developed generalized dystonia after rapid correction of hyponatremia. The second case was a 24-year-old man with gonadotroph pituitary adenoma who developed generalized dystonia, dysarthria, and dysphagia in the course of hyponatremia. Hormonal changes will cause fluctuation in hyponatremia and correction of hyponatremia, even if the recommended rate may be hazardous and will promote ODS. Patients with sellar region tumors are at risk of developing ODS and correction of hyponatremia in these cases should be closely monitored.