Congenital amegakaryocytic thrombocytopenia (CAMT) is an uncommon cause of thrombocytopenia in children. CAMT is characterised by an isolated thrombocytopenia and the near absence of megakaryocytes in the bone marrow. The gene involved in the development of CAMT has recently been described. In a number of CAMT patients, mutations in the thrombopoietin (Tpo) receptor gene, c-mpl, were found to be the likely cause of the thrombocytopenia and the complete bone marrow failure that most patients develop. Measurement of Tpo plasma levels and a study of the megakaryocytopoiesis in vitro, may add to the diagnosis. At present the only curative treatment is allogeneic bone marrow transplantation.