Wernicke's encephalopathy (W.E.), a potentially reversible condition caused by thiamine deficiency, is usually suspected in the setting of chronic alcoholism and might not be recognized when associated with other conditions. We describe a young pregnant woman who presented with rapidly evolving ataxia, diplopia and irrelevant speech following repeated vomiting. Characteristic brain MRI and rapid response to thiamine suggested that she had W.E. possibly due to hyperemesis gravidarum. A high index of suspicion is required, since delayed or lack of treatment may lead to high morbidity and mortality.