Idiopathic thrombocythemia is a rare condition of which about 80 cases have been reported. It was first described by Epstein in 1930,1,2 and the published cases have recently been reviewed by Ozer et al.3 and by Gunz.4 It forms part of the spectrum of myeloproliferative disorders which include polycythemia rubra vera and perhaps leukemia. The distinction between polycythemia vera with excessive production of red cells, and thrombocythemia with excessive production of platelets, is not sharp. The platelet count is raised in 30%-50% of cases of polycythemia,5 and this is probably responsible for the thromboses common in that disease and largely determining its prognosis. Conversely in thrombocythemia the hemoglobin and red blood cell count are often raised, especially after treatment with iron.6 In both conditions there is a leukocytosis, and splenomegaly is common. A small proportion of cases with the clinical picture of thrombocythemia eventually develop