Background: The aim was to evaluate the clinical Alvarado scoring system and computed tomography (CT) criteria for the diagnosis of acute appendicitis. Material/Methods: The study was carried out retrospectively in patients who were referred to the Institute between March 2014 and January 2015. One hundred seventeen patients with acute abdominal pain who underwent abdominal CT were enrolled in this retrospective study. Patient demographics, clinical Alvarado scoring, CT images, and pathologic results of the patients were evaluated. Results: Thirty nine of the 53 patients who were operated on had pathologically proven acute appendicitis. CT criteria of appendiceal diameter, presence of periappendiceal inflammation, fluid, appendicoliths, and white blood cell count (WBC) were significantly correlated with the inflammation of the appendix. The optimal cut-off value of the appendiceal diameter was 6.5 mm. The correlation between appendiceal diameter and WBC was 80% (P=0.01 <0.05). The correlation between appendiceal diameter and Alvarado score was 78.7% (P=0.01 <0.05). Conclusions: Presence of appendiceal diameter above 6.5 mm on CT, periappendiceal inflammation, fluid, and appendicoliths should prompt the diagnosis of acute appendicitis. Since patients with acute appendicitis may not always show the typical signs and symptoms, CT is a helpful imaging modality for patients with relatively low Alvarado scores and leukocytosis, when physical examination is confusing.