Haemophagocytic lymphohistiocytosis (HLH) is an autosomal recessive disease with histiocytic and lymphocytic infiltrations in multiple organs. Cure seems possible only by allogeneic bone marrow transplantation (BMT), but matched sibling donors (MSD) are restricted and high mortality rates are associated with BMT from unrelated donors (URD). We report on 12 consecutive HLH patients with an improved outcome following URD transplants. Eight patients received BMT from URD, four from MSD. Five patients had signs of active HLH at the time of BMT. The conditioning regimen consisted of 20 mg/kg busulphan, 60 mg/kg VP-16 and 120 mg/kg cyclophosphamide and, in case of URD, 90 mg/kg antithymocyte globulin. The doses of busulphan and VP-16 were reduced during the programme to 16 mg/kg and 30 mg/kg, respectively. Using a fivefold graft-versus-host disease (GVHD) prophylaxis, GVHD was absent or mild in 10, and moderate or severe in two patients undergoing unrelated transplants. One patient with URD experienced graft failure and was retransplanted on day 37. Major toxicities were hepatic veno-occlusive disease in five, capillary leak syndrome in two, pneumonia in three, sepsis in one, severe mucositis in one and seizures in two patients. All patients are alive without HLH after a median follow-up of 24.5 months. One patient has chronic GVHD, another patient has severe retardation. Three patients show slight to moderate development delay. These results indicate that in HLH, BMT from matched unrelated donors should be performed. Incomplete resolution of disease activity need not impede a successful outcome.