This clinical policy from the American College of Emergency Physicians is an update of a 2000 clinical policy on the evaluation and management of patients presenting with nontraumatic acute abdominal pain.1 A writing subcommittee reviewed the literature to derive evidence-based recommendations to help clinicians answer the following critical questions: (1)Can clinical findings be used to guide decision making in the risk stratification of patients with possible appendicitis? (2) In adult patients with suspected acute appendicitis who are undergoing a computed tomography scan, what is the role of contrast? (3) In children with suspected acute appendicitis who undergo diagnostic imaging, what are the roles of computed tomography and ultrasound in diagnosing acute appendicitis?Evidence was graded and recommendations were given based on the strength of the available data in the medical literature.