© 2022 Turkish Association of Trauma and Emergency Surgery.BACKGROUND: Acute appendicitis (AA) is the most common reason for pediatric abdominal surgery in the world. Despite advances in science and technology, diagnosing AA is still difficult today, and complications are common as a result. The early prediction of complicated appendicitis is of great importance for the surgical planning, further treatments, and predicting the course of disease. The immature granulocyte (IG) is a new and more effective marker in predicting the severity of inflammation than traditional markers. Our aim is to determine the effectiveness of IG% in the diagnosis and severity of AA. METHODS: Eighty-eight patients diagnosed with AA and a control group of fifty-eight healthy children were included in this prospective study. Patients with pathologically confirmed AA were divided into two subgroups: acute simple appendicitis (ASA) and acute perforated appendicitis (APA). The demographic characteristics, white blood cell (WBC) count, neutrophil-to-lymphocyte ratio (NLR), mean platelet volume (MPV), IG%, and C-reactive protein (CRP) values were analyzed. Receiver operating characteristics (ROC) analysis was used to compare the diagnostic accuracies and predictive performances. RESULTS: Patients with AA had higher IG%, WBC count, NLR, and MPV value than control group (p=0.28, p=0.22, p<0.001, p=0.001, respectively). Only IG% showed statistically significant difference from other inflammatory markers evaluated in ASA and APA patients (p<0.001). ROC analysis showed that IG% is a good predictor for the presence of APA at an optimal cut-off for IG being 0.2% (sensitivity 81.8%, specificity 85.2%, area under the ROC curve 0.83). CONCLUSION: In the present study, we demonstrated that AA patients with higher IG levels might be more likely to develop perforation. The IG values combined with a physical examination, imaging studies, and other laboratory tests may help clinicians to identify high-risk AA patients in the pediatric emergency department.