Essential thrombocythemia (ET) is a clonal disorder of the myeloid stem cell that causes pathologic expansion of the megakaryocytic elements in the bone marrow, with a persistent increase in the platelet count. In order to avoid the mutagenic effects of radioactive phosphorous and alkylating agents, various European clinicians use pipobroman rather than hydroxyurea as single chemotherapeutic treatment, since it is simple and well tolerated and does not lead to hematological complications or the risk of visceral cancer. Here we describe a 63-year-old ET patient who showed myelodysplastic transformation (RAEB-t) of the primary disease after about eight years of therapy with pipobroman at variable dosages.