Hypereosinophilia, either clonal or reactive, has been described in association with multiple hematological malignancies. We describe a case of a patient presenting with hypereosinophilia that evolved into T-cell lymphoblastic lymphoma. Complete remission was achieved with chemotherapy; however, hypereosinophilia recurred 5 months later in association with myeloblastic bone marrow infiltration and without evidence of lymphoblastic lymphoma relapse. Cytogenetic analysis of the bone marrow showed a complex translocation involving chromosomes 7, 12, and 16. A rearrangement of ETV6 gene (12p13) was demonstrated by FISH studies, thus confirming the clonality of this population. The association of lymphoblastic lymphoma, eosinophilia, and myeloid hyperplasia has been described in disorders with FGFR1 rearrangements. We hypothesize that other clonal eosinophilic disorders lacking this rearrangement could behave in a similar fashion through different pathogenic mechanisms.