Central pontine myelinolysis is a demyelinating disease of central pons. Nocturnal polyuria is defined as increased urination during nighttime with a nocturnal fraction exceeding from 20% to 33%. We have experienced nocturnal polyuria developed in two patients with central pontine myelinolysis. In these cases, serum antidiuretic hormone and urine osmolality were lower at nighttime than daytime. It suggests that nocturnal polyuria is caused by abnormal diurnal variation of antidiuretic hormone. In the first case, nocturnal polyuria was recovered spontaneously and also follow up brain MRI showed decreased signal intensity in pons. In the second case, nocturnal polyuria was improved after the treatment of intranasal desmopressin. It appeares that central pontine myelinolysis can cause nocturnal polyuria due to the interruption of antidiuretic hormone pathway. The symptom of nocturnal polyuria can be treated by desmopressin. (J Korean Acad Rehab Med 2007; 31: 356-360)
