A 25-year-old woman with hyperemesis gravidarum developed acute Wernicke's encephalopathy during prolonged intravenous fluid therapy without vitamin supplements. Delay in diagnosis led to a persistent severe neurological deficit, including coma. Gadolinium-diethylenetriaminepentaacetic acid-enhanced magnetic resonance imaging revealed symmetrical lesions around the aqueduct and fourth ventricle, which resolved after treatment with thiamine. She did not regain consciousness. This report demonstrates the diagnostic value of enhanced magnetic resonance imaging in acute Wernicke's encephalopathy.