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Objective: Although autism spectrum disorder (ASD) is one of the most studied neurodevelopmental disorders, its etiology has not been fully elucidated. A growing body of evidence suggest the role of neuroinflammation in the etiology of ASD. Neutrophil to lymphocyte ratio (NLR) and platelet to lymphocyte ratio (PLR) are markers of systemic inflammation. In this study, we aimed to evaluate NLR and PLR in children with ASD comparison to healthy controls. Methods: We reviewed the medical files of children with ASD in the ages of 2 to 5. The ASD group were consisted of drug-naïve 64 children who had complete blood count within a month of assessment. Age and sex matched 64 healthy children without any psychiatric disorders were recruited from the healthy child outpatient unit of the hospital. Results: NLRs were significantly higher in ASD. Children with ASD had significantly higher neutrophil counts but lower platelet and lymphocyte counts compared to those of healthy controls. NLR was found to be a predictor of ASD. Conclusions: Increased NLRs support the hypothesis of the involvement of neuroinflammation in the under-lying physiopathology of ASD. Even though recent evidence is not enough to suggest that in young children increased NLR levels may be used as screening and early intervention predictor, it should be kept in mind and may inspire new studies. Further longitudinal studies with larger sample size and homogeneous groups regarding the age and subtypes may clarify the inflammatory involvement in ASD. [Anadolu Psikiyatri Derg 2018; 19(6.000): 607-614]