Introduction: Wernicke’s encephalopathy (WE) is a neuropsychiatric complication of bariatric surgery (BS) due to vitamin B1 deficiency, whose early presentation is infrequent and underdiagnosed. Aim: To present a case of early WE after laparoscopic gastric bypass (LGB) and discuss its diagnosis, complications and treatment. Materials and Methods: A 23-year-old obese woman on whom a LGB was performed, from the fourth postoperative day presented with nausea, cough, drooling, abdominal discomfort, and irritability. The imaging and endoscopic study ruled out surgical complications. WE is suspected, so a brain MRI is taken, resulting in normal. However, after a thiamine load the symptoms resolve. Results and Discussion: Vomiting, surgery, and the physiologically limited reserve of B1 determined an early onset of WE, which typically occurs between 4 and 12 weeks in BS. Classical symptoms and its imaging findings are present in the minority of patients. WE is a rare but potentially serious complication in BS even with irreversible memory damage. The growing volume of BS has increased its incidence. An adequate supple-mentation and diagnostic suspicion are key for its prevention and early treatment.