Complications of bariatric operations include the development of nutritional deficiencies. If protracted vomiting is added, severe vitamin depletion could arise such as thiamine deficiency, resulting in the development of Wernicke's encephalopathy (WE). This article describes the rapid onset of WE in a 6-week postoperative morbidly obese woman. Because the occurrence of micronutrient deficiencies is infrequent, although reports are increasing, symptoms may be misdiagnosed leading to possible irreversible effects on the central nervous system. The importance of a prompt diagnosis of this serious complication and of adequate therapy is emphasized.