Abstract: This study was conducted to assess the efficacy of ultrasound in the diagnosis of acute appendicitis in clinically suspected cases of acute appendicitis. A total of 110 patients clinically suspected to have acute appendicitis admitted to the surgery departments of Golestan and Imam Khomeini hospitals, from March 2006 to 2007. Abdomino-pelvic ultrasonography with focus on RLQ ultrasonographying the graded compression technique was done. Positive ultrasonography was defined as at least one of the criteria of puylaert. The sonographic data were prospectively correlated with clinical, operative and pathological findings. Graded compression ultrasonography results were analyzed and remarked 92.7% sensitivity, 94.5% specificity, 93% accuracy, 94.4% positive predictive value and 92.5% negative predictive value. Ultrasonography is an accurate, safe and reliable method in the diagnosis of suspected cases of acute appendicitis that can help to minimize negative appendectomies and perforation rates.