A 24-year-old woman developed hyperemesis gravidarum, complicated by Wernicke's encephalopathy and central pontine myelinolysis. The first-was due to a deficiency of thiamine, and was hastened by intravenous dextrose without thiamine supplements. However, no changes in serum sodium or phosphorus values were observed. In this case, the pathophysiology of central pontine myelinolysis remained obscure.