Wernicke-Korsakoff's syndrome (W.K.S.) is a complication of alcoholism and malnutrition and usually presents acutely and is characterized by disturbances of consciousness, paralysis of the external ocular muscles, ataxia and disorder of retentive memory. The disease results from deficiency of vitamin B1, or thiamine, an essential coenzyme in intermediate carbohydrate metabolism. We report a seriously ill, nonalcoholic surgical patient, who developed W.K.S. in the postoperative period as a result of thiamine deficiency, during prolonged intravenous therapy. It is recommended that malnourished patients receive 100 mg parenteral thiamine especially when glucose infusions are administered.