Essential thrombocythemia (ET) and chronic lymphocytic leukemia (CLL) are 2 distinct, clonal hematologic malignancies. The association of ET and CLL is very rare, and only a handful of cases have been described in the literature, the pathogenic mechanisms of this phenomenon remain unclear. Here we describe a patient with an uncommon case of Janus Kinase 2 (JAK2) V617F positive ET treated by hydroxyurea and pipobroman, who eventually developed a second unrelated hematologic malignancy, CLL