Wernicke's encephalopathy (WE) is an acute neuropsychiatric condition due to thiamine deficiency (vitamin B1) most commonly associated with chronic alcohol abuse. WE is difficult to diagnose because the classical triad of signs (confusion, ataxia and ophthalmoplegia) occurs in only 10% of cases. The presentation is often one of a non-specific confusional state which may easily be attributed to intoxication, alcohol withdrawal or to a concurrent morbidity such as head injury. To improve the outcome, it is important to make a presumptive diagnosis of WE and treat the patients as soon as possible with high-dose parenteral thiamine. Patients with an alcohol problem associated with malnutrition should all be offered a preventive treatment with parenteral thiamine in view of the impaired oral thiamine absorption.