OBJECTIVE A systematic literature review was performed to evaluate the effectiveness of abdominal sonography and abdominal computed tomography (CT) in diagnosing acute appendicitis in adult and pediatric patients. METHODS Peer-reviewed literature published between 1986 and 2014 was searched using multiple medical literature databases. Studies included in this review were conducted on human patients; included more than 50 patients; reported diagnostic values; evaluated pediatric patients, adults, or both (pregnant women excluded); and used histological results from surgery or clinical follow-up as a reference standard. RESULTS In the sonography studies, the calculated pooled values of sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 86%, 94%, 100%, and 92%, respectively. In the CT studies, the calculated pooled values of sensitivity, specificity, PPV, and NPV were 95%, 94%, 95%, and 99%, respectively. CONCLUSIONS Unenhanced CT is used frequently to minimize harmful effects of radiation, especially for pediatric patients. Performing sonography can reduce the cost of a negative exploration, which can generate unnecessary financial burdens for patients. CONCLUSIONS This study suggests that sonography is an effective first-line diagnostic tool for acute appendicitis and that CT should be performed for patients with inconclusive sonographic findings.