Objective: Patients with persistent eosinophilia may have many conditions ranging from relatively benign diseases such as parasitic serious infections to life-threatening serious diseases. We aimed to determine the etiological causes of hypereosinophilia in children. Material and Methods:Patients under 18 years of age who had complete blood counts in Ankara Child Health and Diseases Hematology Oncology Training and Research Hospital's pediatric clinics between January 2013-January 2016 were retrospectively analyzed. Hypereosinophilia was defined as having at least two peripheral blood absolute eosinophil counts greater than or equal to 1500/mm 3 .The results of the examinations and diagnoses when the patients were detected with hypereosinophilia were recorded from the hospital records.Results: Three hundred and forty patients who underwent complete blood count were found to have hypereosinophilia. Seventy patients whose file records could not be accessed were excluded from the study. Two-hundred seventy patients (56% male) with a median age of 5 (IQR:1-12) years were included in our study. When the diagnoses of patients were examined, 48 (17.8%) had allergic diseases, 21 (7.8%) had immunodeficiency, 14 (5.2%) had parasitic disease. 15 (5.5%) had tumor, 4 (1.5%) had leukemia, 2 (0.7%) had hypereosinophilic syndrome, 2 (0.7%) had adrenal insufficiency