Wernicke's encephalopathy is commonly associated with chronic alcohol abuse, but may also occur in patients with poor nutritional status. We report a case of acute Wernicke's encephalopathy in a patient with AIDS without any predisposing risk factors for thiamine deficiency. In developing countries, without vitamin supplementation, this disorder may play a role in the morbidity and mortality associated with AIDS. We believe that thiamine supplementation should be considered in cachetic AIDS patients, especially where access to antiretroviral therapy is limited.