Plasma cell leukemia (PCL) is a rare aggressive lymphoproliferative disease with a short median survival and a very poor prognosis. We report the case of a 63-year-old man who developed a PCL after 5 years of chemotherapy with hydroxyurea and busulphan for Essential thrombocythemia (ET). The karyotype showed a deletion of chromosome 7 and the plasma cells cytofluorimetric examination revealed a high expression of Multidrug Resistance related P-glycoprotein (PGP). After the second cycle of VAD chemotherapy the patient had a severe pneumonia and died with refractory PCL. This is a rare example of the coexistence of a chronic myeloproliferative and lymphoproliferative diseases in the same patient, and to the best of our knowledge, the first reported in the literature involving PCL and ET. Moreover, this case shows the possibility of secondary malignancies developing in patients treated with busulphan and hydroxyurea for chronic myeloproliferative disorders.