Congenital amegakaryocytic thrombocytopenia (CAT), a rare syndrome with failure of megakaryopoiesis, cannot be cured by immunoglobulins, steroids or cyclosporin, but only by allogeneic bone marrow transplantation (BMT). We report on eight patients with CAT, all of whom were dependent at the time of BMT on platelet transfusion. Sources of haematopoietic progenitor cells were bone marrow (n = 5), peripheral stem cells (n = 2) and cord blood (n = 1). Seven patients engrafted. Both patients with matched unrelated donor transplants died, six patients are well with stable platelet counts 3-27 months after transplantation. BMT represents a curative option for CAT. The benefit of using alternative marrow donors should be carefully evaluated.