The purpose of this study was to determine which clinical information or computed tomography (CT) features can distinguish perforated from nonperforated appendicitis. We collected data from 102 patients (62 men, 40 women; mean age, 49.6 years; age range, 16-85 years) who presented to the emergency department with acute abdominal pain or suspicion of acute appendicitis and underwent appendectomy. In the clinical information, there was no significant factor to predict appendiceal perforation. As for CT features, significant imaging factors for predicting appendiceal perforation included abscess, phlegmon, and thickening of lateroconal fascia. The treatment strategy of acute appendicitis varies according to the integrity of the appendiceal wall. Besides clinical findings, CT features can distinguish perforated from nonperforated appendicitis, facilitating proper decision making in ER.