Background: Leukemias are among the most common childhood malignancies. Acute lymphoblastic leukemia (ALL) accounts for 77% of all leukemias. In rare cases, ALL patients may present with eosinophilia.
Case Report: Here, a 5-year old boy was admitted to our hospital with a possible diagnosis of appendicitis. This patient’s complete blood cell count demonstrated leukocytosis with severe eosinophilia. Following a 1-month clinical investigation, 2 bone marrow aspirations, and flow cytometry analysis, a diagnosis of acute lymphoblastic leukemia was proposed. Finally, the patient was transferred to the oncology ward to receive standard therapeutic protocol, which resulted in disease remission. After chemotherapy for 2 years, patient is successfully treated.
Conclusions: ALL is diagnosed by eosinophilia in rare cases. These patients need immediate diagnosis and intensive therapy due to worsened prognosis of ALL presenting as hypereosinophilia.

Keywords: Eosinophilia, acute lymphoblastic leukemia, eosinophilic myelodysplasia