Wernicke's encephalopathy (WE) is a neuropsychiatric syndrome due to thiamine deficiency, which is potentially fatal but preventable. In Obstetrics, it can complicate hyperemesis gravidarum because of major daily requirement. Nowadays there is no consensus on early diagnosis, treatment and prevention of this disorder. We present a case report of hyperemesis gravidarum which degenerated into WE and Korsakoff's syndrome. It highlights that the clinical suspicion is necessary to recognize signs and symptoms, to apply the available effective preventive measures in situations at risk and to begin urgent treatment in presence of characteristic clinical features.