Peripheral blood eosinophilia as a presentation of acute lymphoblastic leukemia (ALL) has only rarely been reported. The eosinophilia is thought to be a nonneoplastic reaction to the neoplastic lymphoblasts. We present the case of a 5-year-old girl who developed peripheral hypereosinophilia with no circulating blasts prior to her diagnosis of B-cell lineage ALL. Cytogenetic study showed a hyperdiploid blast population with 5q deletion. Persistent peripheral hypereosinophilia should always be fully investigated, the possibility of a malignancy including ALL needs to be excluded, even in the absence of peripheral cytopenias and circulating blasts.