Objective: Congenital hematological disorders are frequently observed in patients with Down syndrome (DS). In this study, we aimed to investigate peripheral blood-derived inflammation biomarkers such as neutrophil-lymphocyte ratio, platelet-lymphocyte ratio, and eosinophil-monocyte ratio in patients with Down syndrome. Material and Methods: Ninety-eight patients with karyotypically ascertained DS and 103 healthy controls were included. All subjects were divided into three age groups: 0-2 years (34 patients, 34 controls), 2-6 years (32 patients, 33 controls), and >6 years (32 patients, 36 controls). Demographic, clinical, and laboratory data of patients with DS who were admitted between June 2010 and December 2021 were reviewed from the file records from the pediatric allergy and immunology department. Results: Lymphocyte, eosinophil, and eosinophil-monocyte ratio were found to be significantly lower in children with DS compared to controls in group 2 (2-6 years) and group 3 (>6 years). Platelet-lymphocyte ratio was found to be higher in children with DS in group 2 and group 3. There was no statistically significant difference between DS and controls in group 1 (<2 years) in terms of all parameters. In group 2 (2-6 years) and group 3 (>6 years), there was a statistically significant difference between DS and controls in terms of lymphocyte, eosinophil, platelet-lymphocyte ratio, and eosinophil-monocyte ratio variables (P>0.05). Conclusion: We found significant differences among lymphocyte, eosinophil, platelet-lymphocyte ratio, and eosinophil-monocyte ratio in patients with DS. As a result, these parameters should be evaluated carefully for clinical outcomes.