During a 12-month period high-resolution, real-time ultrasonography (US) with graded compression was performed on 268 consecutive patients with clinically suspected acute appendicitis and its complication. US visualization of a fluid-filled, non-compressed appendix or a decompressed, thick-walled appendix was the primary criterion for a diagnosis of acute appendicitis. The sonographic findings were correlated with surgical-pathologic outcome in 92 cases and with the findings of clinical follow-up in the remainder. US was found to be accurate in the diagnosis of acute appendicitis and its complication with a sensitivity of 93.3%, a specificity of 98.9%, and an accuracy of 97%. The predictive value of a positive test was 97.7%; that of a negative test was 96.7%. There were two false-positive examination in patients with a thick-walled appendix or periapperdiceal abscess, which were surgically confirmed as appendiceal adenocarcinoma and perforated cecal diverticulitis respectively. There were six false-negative examination in patients with a sonographically no-visible appendix, which were confirmed surgically as acute appendicitis(n=5) and perforated appendicitis(n=1). Our results show that high-resolution, real-time US is an accureate imaging modality in the diagnosis of acute appendicitis and the evaluation of its complication.