For the evaluation of acute appendicitis, many diagnostic methods, such as physical examination, laboratoryfindings, plain abdomen and barium enema have been widely used. But the overall accuracy was ranged from 50% to 84% and negative appedectomy rate was reported between 5% and 35%. In these days, high resolusion ultrasonographyis well known to be a good imaging modality in evaluation of acute appendicitis and its complications. Using highresolution ultrasonography, 138 patients with right lower quadrant abdominal pain were examined for 16 months. Theresults were compared to post-operative findings and clinical follow up study. The results were as follows: 1. Thesex distribution of cases were 58 males and 80 females, and most common in the third decade (33.3%). 2. Thepositive ultrasonographic findings were in 69 cases (50%), those were simple appendicitis without complication in46 cases (66.7%), acute appendicitis with periappendicitis in 9 cases (13.0%), acute appendicitis withappendicolith in 4 cases (5.8%) and perforated appendicitis in 4 cases (16%). 3. The ultrasonographic findings ofnormal appendix were in 69 cases (50%), those were nonvisualization of appendix in 62 cases (91.3%) andvisualization of normal appendix with single thin echogenic wall in 6 cases (8.7%). 4. In the 50 cases of controlgroup, the visualization of normal appendix on ultrasonography were in 8 cases (16%). 5. The overall accuracy was95.7% with 97.1% of sensitivity and 94.4% of specificity.