We report a 74-year-old man with Wernicke's encephalopathy (WE) whose only prior illness was peptic ulcer disease. Upper gastrointestinal endoscopy demonstrated gastric ulcer scars accompanied by marked deformity, without pathologic evidence of malignancy. WE due to peptic ulcer disease in previous reports was substantially associated with thiamine deficiency due to recurrent vomiting or surgical procedures. In our case, however, there was no history of vomiting or gastrointestinal surgery. Besides, we thoroughly ruled out other known clinical settings related to WE. There is the possibility that peptic ulcer disease itself provoked thiamine deficiency due to malabsorption.