Aim. The aim was to evaluate the clinical Alvarado scoring system and computed tomography (CT) criteria for the diagnosis of acute appendicitis. Material and Methods. 117 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. 39 of the 53 patients who were operated on had pathologically proven acute appendicitis. CT criteria of appendiceal diameter, presence of periappendiceal inflammation, fluid, appendicolith, and white blood cell (WBC) count were significantly correlated with the inflammation of the appendix. The best cut-off value for appendiceal diameter was 6.5 mm. The correlation between appendiceal diameter and WBC count was 80% (P = 0.01 < 0.05). The correlation between appendiceal diameter and Alvarado score was 78.7% (P = 0.01 < 0.05). Conclusion. Presence of CT criteria of appendiceal diameter above 6.5 mm, periappendiceal inflammation, fluid, and appendicolith 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 score and leukocytosis and when physical examination is confusing.