••Amegakaryocytic Thrombocytopenia (AMT) is characterized by severe persistent thrombocytopenia and markedly decreased to absent megakaryocytes presenting with bleeding symptoms ranging from purpura to intracranial hemorrhage (ICH). Unlike children with Thrombocytopenia with Absent Radii (TAR), AMT patients are more heterogeneous and often progress to marrow aplasia. Only 51 published cases of “AMT” were identified. Based on specific diagnostic criteria, 22 so-called cases of AMT were excluded: 10 neonates with rapid resolution; rubella-2; severe cardiac defects-4; sepsis-2; TAR-1; and 3 cases without bone marrow examination. Of the 29“true” AMT cases, 10 had congenital anomalies with 6 of 10 having multiple anomalies, primarily neurologic (6) and orthopedic (5). Children with anomalies were diagnosed within the first year of life, while the 19 without anomalies were diagnosed as late as 3 years of age. Seventeen of 29 patients had progression to marrow aplasia at a median age of 4 years: 4 with anomalies at a median of 19 mos, 13 without anomalies at a median of 5 yrs. One child progressed from AMT to ANLL; 1 infant with apparent AMT progressed rapidly to MDS and then to ANLL. Another child had a sibling with leukemia. All patients had bleeding problems and most received platelet transfusions. Fifteen of the 29 patients died of: ICH-5 (median age 3 yrs, 4 mos; range 4 days to 4 years); aplasia-6; and other-4. We have just completed a case survey in which information was accrued on 24 children with AMT and 48 with TAR to better characterize the natural history and current outcome of these patients. This new data will supplement the published information reported in this abstract.