The occurrence of polymyositis (PM) correlates with an increased risk of solid tumor. Among hematologic malignancies that are sporadically associated with PM or dermatopolymyositis (DM), lymphoma and chronic lymphoid leukemia are the most frequent. The association between PM and myeloproliferative disorders remains exceptional. We describe the simultaneous revelation of a PM and an essential thrombocytemia (ET). The sensitivity of the PM to corticosteroids was noteworthy and allowed a quick and definitive control of clinical and biological inflammation. Despite the efficiency of a cytostatic agent upon the thrombocytemia, the patient died after numerous thrombotic and hemorrhagic complications of ET. This is the first published case of such an association between PM and TE. The paraneoplastic significance of the PM is discussed.