Two thrombocytopenic infants with essentially normal initial bone marrow morphology were believed to have idiopathic thrombocytopenic purpura. However, they failed to respond to steroids and intravenous immunoglobulins and had a normal platelet recovery after transfusions. The diagnosis was revised to congenital amegakaryocytic thrombocytopenia after bone marrow biopsies, which revealed a marked paucity of megakaryocytes. Repeated biopsies disclosed gradually decreasing numbers of megakaryocytes and increasing marrow hypoplasia. At the ages of 42 and 22 months the children underwent allogeneic bone marrow transplants, one of them with an unrelated marrow donor. Both patients are well with good engraftment of donor marrow and normal peripheral blood counts, 31 and 12 months after BMT, respectively.