The number of patients submitted to bariatric surgery to treat morbid obesity is increasing, therefore, some nutritional deficiencies, with which many physicians are no longer familiarized, are reappearing. Postoperatively, many nutritional disorders may occur, one of them is thiamine deficiency (beriberi). The thiamine and/or vitamin B12 deficiency can correspond to 40% of the neuropathy cases after bariatric surgery. Two patients with the clinic of peripheral neuropathy and Wernicke-Korsakoff syndrome will be reported. Some months after the surgery, they presented prostration, depression, mental confusion and nystagmus, associated with pain and paresthesia in limbs (especially lower limbs). With the diagnostic hypothesis of beriberi, the treatment with thiamine started. One of the patients presented complete improvement of the neurological symptoms, however the other one remained with motor deficiency, exactly the one who spent a longer period of time between the symptoms appearance and the treatment beginning. These cases serve to alert us about the importance of nutritional vigilance after bariatric surgery.