Allogeneic bone marrow transplantation represents the treatment of choice for severe bone marrow failure in patients with Fanconi's anaemia (FA). In view of the increased sensitivity to alkylating agents documented in this condition, much attention has focused on reducing the conditioning chemotherapy. We present a 13-year-old girl in whom sibling allogeneic BMT after conditioning with low-dose cyclophosphamide only resulted in graft rejection. However, a second transplant using the same donor proved successful following a more intensive conditioning regimen. This case demonstrates the phenotypic variability of FA, and highlights the need for tailoring the conditioning regimen for a given patient.