Wernicke's encephalopathy is an acute neurolopsychiatric syndrome caused by 
thiamine deficiency, and classically presents with the triad of opthalmopathy, 
ataxia and altered mentality. Both prolonged total parenteral nutrition and 
reduced oral intake can induce Wernicke's encephalopathy during hematopoietic 
stem cell transplantation (HSCT). Although early treatment is important for 
recovery from Wernicke's encephalopathy, the vague symptoms and characteristics 
hinder early diagnosis. Furthermore, Wernicke's encephalopathy is not infrequent 
and can develop at any age during HSCT. Herein, we present two young patients 
developing Wernicke's encephalopathy during HSCT.