Objectives: This study is an evaluation of the accuracy of ultrasonography (USG), computed tomography (CT), and Alvarado score (AS) in the diagnosis and management of acute appendicitis in children. Methods: Records of pediatric patients admitted to the pediatric emergency department (ED) between 2008 and 2012 were evaluated retrospectively. Patient data from the national electronic health information system was screened and those with complete clinical and imaging findings (AS, preoperative USG and/or CT images) and postoperative pathological diagnosis were included in the study. Results: Study group consisted of 449 children with diagnosis of suspected acute appendicitis aged between 3 and 15 years (mean age: 9.20 ± 2.73 years). Of the total, 428 (95.3%) patients underwent appendectomy and 21 (4.7%) cases were treated conservatively. Mean duration of symptoms was 4.94±1.84 hours. Pathological evaluation results were negative (i.e., removal of normal appendix) in 36 (8.4%) patients; histopathological diagnosis was acute appendicitis in 392 (91.6%) patients. Perforated appendix was found in 38 (8.5%) patients. In patients with histopathologically confirmed appendicitis, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of CT in diagnosis of acute appendicitis were 96.3%, 55.6%, 92.8%, and 71.4%, respectively. Sensitivity, specificity, PPV, and NPV of USG were 73.5%, 22.2%, 91.1%, and 69.2%, respectively. Negative appendectomy rate was 6.4% (n = 8) in patients who had preoperative CT scan, and 6.5% (n = 28) in patients who had USG examination. Conclusions: CT has higher sensitivity than USG in diagnosis of acute appendicitis. USG, on the other hand, is widely accessible method and does not use ionizing radiation. Therefore, it may be used as initial radiological imaging method in acute appendicitis. Thin-filter, contrast-unenhanced CT scans may be preferred in cases where clinical signs and USG findings are unclear or controversial.