Glanzmann's thrombasthenia is an autosomal recessive disorder characterized by a lack of platelet aggregation due to the absence of platelet glycoprotein IIb and IIIa. Usually, the disease leads to mild hemorrhage but sometimes bleeding is severe enough to be life-threatening. We report the case of a 16-year-old girl, presenting with very severe type 1 Glanzmann's thrombasthenia, successfully treated with an HLA-identical sibling bone marrow transplant (BMT). We also update the clinical and laboratory data of her brother, who had received a BMT 16 years ago for the same disease. In the light of these two cases and two others published in the literature, we discuss the indications for BMT from HLA-identical sibling donors in Glanzmann's thrombasthenia. Alloimmunization against the missing platelet GPIIb/IIIa complex and severity of bleeding episodes may constitute sufficient criteria for allogeneic BMT after careful assessment of the risk-benefit of such a procedure, although this remains exceptional in this disease. Bone Marrow Transplantation (2000) 25, 327-330.