An eight-year-old boy with Fanconi's anaemia received a bone marrow transplantation from an unrelated donor. Sustained engraftment was achieved, but he developed major complications including acute grade III graft-versus-host disease, autoimmune haemolytic anaemia with positive Coombs' test and free antibodies against Rhesus group, and a virus-associated haemophagocytic syndrome; this latter complication was successfully treated with acyclovir. Sixteen months after transplantation he has full haematopoietic reconstitution, but with persisting mild autoimmune haemolysis.