Wernicke's encephalopathy is an acute neuropsychiatric condition due to thiamine deficiency frequently associated with chronic alcohol abuse. We describe 2 cases of patients who experienced acute Wernicke's encephalopathy after allogeneic stem cell transplantation associated with the use of commercial total parental nutrition. Early diagnosis with magnetic resonance imaging and timely treatment with thiamine resulted in rapid resolution of clinical and radiological signs. In conclusion, the prolonged use of commercial total parental nutrition formulas must be supplemented with thiamine in the form of intramuscularly administered multivitamins.