A 37-year-old woman with a history of transphenoidal surgery and gamma knife treatment for prolactinoma was admitted because of pneumoniae with hyponatremia (Na 109 mmol/l). After the careful correction of the serum sodium level within 15 mmol/l/day, the patient developed parkinsonism. MRI of the brain disclosed a signal increase in the bilateral basal ganglias on T2-weighted images, a finding consistent with extrapontine myelinolysis (EPM). Interestingly, the parkinsonism fully disappeared after the replacement therapy of hydrocortisone for adrenal insufficiency due to hypopituitarism, and MRI 5 months later showed complete disappearance of the lesions, indicating the patient had ameliorated from the EPM.