A report of 33 years old female with Wernicke's encephalopathy is presented. The disease was secondary to hyperemesis gravidarum, started from the 6th week of pregnancy. Neurological symptoms as nystagmus, headache, vertigo, disturbance of consciousness and ataxia are described, as well as difficulties in finding out the right diagnosis. We present the therapy with vitamin B1. The subsequent course of the pregnancy was uncomplicated and resulted in a birth--by caesarean section of a healthy male infant, weighted 2790 grams. However, four months later after the delivery, the patient is not yet completely recovered and still demands thiamine supplementation.