Hypermesis gravidarum is a complication defined as vomiting severe enough to require hospital admission during early pregnancy. Thiamine deficiency is known to lead to certain neurological seguelae including Wernicke-Korsakoff syndrome. Wernicke's encephalopathy is an illness of acute onset characterized by global confusion, paralysis of eye ball movements, and gate ataxia due to a deficiency of thiamine. The immediate administration of thiamine prevents progression of the disease and reverses brain lesions that have not yet progressed to the point of fixed structural change. We have experienced a case of Wernicke-Korsakoff syndrome associated with hyperemesis gravidarum, which seemed to be developed by prolonged thiamine-free fluid therapy. We emphasize the need for thiamine supplementation in hyperemesis gravidarum patients.