Our patient has been followed up at Children's Hospital of Pittsburgh, Pittsburgh, Pa. He had several episodes of reactive thrombocytosis. The original bone marrow aspirates and biopsy specimens were performed to exclude a myelodysplasia. A mild increase of reticulin in the bone marrow biopsy specimen is a common finding in hypercellular marrows. The increase in megakaryocytes was interpreted as reactive, because it was associated with thrombocytosis. Thrombocytosis is not the usual finding associated with myelofibrosis, but it can be associated with acute megakaryocytic leukemia or essential thrombocythemia demonstrated or resulted in a normal karyotype. Even though we considered the possibility of a myelodysplastic process, none of our studies or the clinical course of this patient has so far supported that diagnosis.