A 38-year-old woman was admitted in a psychiatric hospital because of memory disorders. Dry beriberi and Korsakoff's syndrome, as a late neuropsychiatric manifestation of Wernicke's encephalopathy, were established. The beriberi symptoms decreased slowly, but the patient’s memory impairments persisted. These clinical features were caused by a thiamine deficiency. Gastric bypass surgery is associated with an increased risk of thiamine deficiency. Excessive alcohol consumption and poor compliance with vitamin deficiency treatment both contributed to the rapid onset of these disorders. The case we describe demonstrates how important it is that patients who have undergone bariatric surgery are prescribed the correct vitamin supplements and that the treatment is continued for an appropriate period of time; this treatment is particularly important in the case of patients who are also suffering from an comorbid alcohol-related disorder.