Objective: Dynamic changes in the number of eosinophils are observed during the diagnosis and follow-up in coronavirus disease-2019 (COVID-19). Our aim was to show the role of the absolute eosinophil count in the diagnosis of COVID-19 and the relationship with disease severity and prognosis. Methods: In this study, 191 patients (130 inpatients, 61 outpatients) diagnosed with COVID-19 pneumonia with the polymerase chain reaction test and lung computed tomography; and 22 patients with positive influenza test were included as the control group. All demographic, biochemical data, clinical and radiological characteristics were recorded. Results: The mean eosinophils on first day of the inpatient COVID-19 group were found to be statistically lower than the influenza group and the ambulatory groups (p=0.001, p=0.0001). Conclusion: A low eosinophil count in complete blood count, can aid in the early diagnosis of infection. Persistent eosinopenia progresses with disease severity and may help determine the prognosis of the disease. [ABSTRACT FROM AUTHOR]