The authors present one case of Wernicke's encephalopathy in a patient with obstructive pyloric syndrome caused by gastric adenocarcinoma, without previous history of alcoholism or malnutrition. They comment on the importance of physiological aspects of thiamine as a co-enzyme of transketolase and pyruvate-decarboxilase in the metabolic pathway for ATP production and the possibility of existing an interaction between genetical and environmental factors in the onset the symptoms. They draw attention for the clinical diagnosis, which should be precocious for the therapy with thiamine to be effective, especially in patients without previous history of alcoholism or malnutrition.