Malabsorptive syndromes and micronutrient deficiencies represent well-known long-term complications of bariatric surgery. Wernicke's encephalopathy (WE), a neurologic manifestation of thiamine deficiency, has been classically associated with alcoholism or severe malnutrition, but rarely reported after bariatric surgery. Herein, we describe the case of a 27-year-old woman that developed WE 10 months after laparoscopic Roux-en-Y gastric bypass for morbid obesity that was initially misdiagnosed with a consequent retard in the appropriate treatment. Although only a few sporadic cases have been reported in the literature, all surgeons and physicians involved in the care of bariatric patients must be aware of this potentially serious complication.