We report a rare case of Wernicke encephalopathy (WE) in a 35-year-old woman with hyperemesis gravidarum (HG). Initially, the disease manifested as passivity, a loss of interest, sleeping too much, apathy and disorientation. The correct diagnosis was established after the detection of typical pathological findings of WE in the thalamus by magnetic resonance imaging (MRI), which was indicated for the appearance of eye symptomatology in the form of nystagmus. Subsequent treatment with thiamine led to rapid improvement in the patient's clinical status and a favorable course of pregnancy.