Purpose: This study evaluated the usefulness of a new scoring system in diagnosing acute appendicitis which expresses the patient's symptoms, physical examination, and laboratory findings more clearly and objectively. Methods: A prospective study was conducted with 314 patients who were hospitalized with suspicion of acute appendicitis. After analyzing the symptoms, physical examination, and laboratory findings, 10 meaningful variables were selected, each of which were scored separately. The diagnostic value of the new scoring system was evaluated, and analyzed in comparison to the preexisting Alvarado score. Results: Ten variables including vomiting, migration pain, fever, Dunphy's sign, Rovsing's sign, tenderness, rebound tenderness, increased white blood cell counts, increased neutrophil proportion, and increased CRP levels were associated with acute appendicitis. The new scoring system is developed by applying 1 point for each variable, with a total score of 10 points. In the new scoring system, a score above 5 points had sensitivity of 0.75, specificity of 0.73, positive predictive value of 0.92, and diagnostic accuracy of 0.71. The area under the receiver operating characteristic curve was 0.80, which is larger than 0.72 of the preexisting Alvarado score, and thus has a higher diagnostic accuracy. As acute appendicitis progresses, the average score tends to become significantly higher (P=0.001). Conclusion:The new scoring system, which objectively reflects the clinical variables of the patient's symptoms, physical examination and laboratory findings, will be useful in accurately diagnosing acute appendicitis and in quickly deciding a therapeutic policy in patients with right lower abdominal pain. (J Korean Surg Soc 2010;79:207-214)