A 41-year-old male patient with acute myelogenous leukemia and past history of Behcet′s disease received allogenic hematopoietic stem cell transplantation. Tacrolimus 2. 5-3. 0 mg/ 24 h was administered through continuous intravenous pump and the serum level was 10. 0-15. 0 ng/ ml. On day 30, the patient experienced severe delirium manifesting as anxiety,color vision defects,irrelevant answer,and losing the ability to calculate and hypoorientation. On day 33,serum tacrolimus level was maintained at 6. 0-7. 5 ng/ ml,but the patient′s mental symptoms was not improved. The next day,tacrolimus was stopped,the delirium was relieved. On day 35,he switched to oral tacrolimus (the initial dose 1 mg twice daily,on day 7,the dose was adjusted to 2 mg twice daily). On day 10 of oral tacrolimus,he developed consciousness disorder again with refusing to eat. Therefore oral tacrolimus was stopped,an IV infusion of cyclosporine 125 mg twice daily was given. On day 2,the symptom of delirium appeared again,accompanied by self harming behavior. On day 5,cyclosporine was withdrawn and he returned to normal consciousness. After that, rapamycin 1 mg twice daily was orally administered. The delirium did not recur.