Three patients who developed acute onset of cerebral blindness within 5-47 days of BMT using tacrolimus (FK506) as primary GVHD prophylaxis are described. This syndrome has been described with the use of cyclosporin A (CsA) and FK506 in solid organ transplant recipients. CsA-induced cerebral blindness has also been noted in BMT recipients but to date there have been no reports of this complication in BMT patients receiving FK506. We have noted a striking similarity in the clinical and radiographic presentations between these patients and those with CsA-associated cerebral blindness. Reversibility within 1-2 weeks of onset and the potential for substitution of CsA for FK506 in these patients is described.