Hyperemesis gravidarum is a complication defined as nausea and vomiting during early pregnancy. Wernickes encephalopathy is an illness of acute onset characterized by mental disturbance, paralysis of eye movements, and ataxia of gait cause by thiamine deficiency. We recently experienced a case of Wernickes encephalopalhy due to hyperemesis gravidarum, which is treated by administration of thiamine even though outcome of serious healthy problem to both mother and fetus, and reported it with a brief review of the literature.