Wernicke's encephalopathy has been sporadically reported in patients with severe hyperemesis gravidarum. We report a new case of Wernicke's encephalopathy in a patient who had hyperemesis gravidarum associated with signs and symptoms of dry and wet beriberi. The case was managed with very large doses of thiamine. The conclusion was that, in long-lasting hyperemesis gravidarum, recognizing signs of beriberi may help prevent the onset of Wernicke's encephalopathy, thanks to timely therapy with thiamine supplements. A thiamine therapy similar to the one reported in this article could prove useful in long-lasting hyperemesis gravidarum complicated by Wernicke's encephalopathy.