PURPOSE:To evaluate the role of unenhanced CT in diagnosing the acute appendicitis. METHOD AND MATERIALS: We retrospectively analyzed conventional contrast-enhanced abdominal CT scans of 197 normal patients and barium enemas of 26 out of the 197 patients. Additional unenhanced CT scans of right lower abdomen were performed on 30 patients who were suspected of having acute appendicitis;barium enema was performed in 26 patients. RESULTS: in the analysis of the conventional CT scans, we could detect 132(67%) normal appendicies. On barium enema of 26 out of 197 patients, abruptly narrowed appendix was visualized in 5 cases and luminal irregularity in 4 cases but all 26 cases showed normal appendix on CT. In the 30 cases of unenhanced CT, all appendicies were visualized. Among 12 Cases which were proved as acute appendicitis, barium enenma was done in 10 case;abruptly narrowed appendix was shown in 3 and luminal irregularity in 1. Among 18 cases which were diagnosed as normal appendix, nonvisualization of appendix' was in 1 case, abruptly narrowed lumen in 3, and luminal irregularity in 9. CONCLUSION:Unenhanced CT in the area of the cecum may be an effective and safe diagnostic tool for acute appendicitis.