Objective To investigate the value of ultrasound examination in the diagnosis of acute appendicitis. Methods Emergency abdominal ultrasound examination was performed on 152 children who had clinically suspected acute appendicitis. Results Sixty-three children were diagnosed as acute appendicitis by ultrasound . Among them, fifty-nine children had emergency appendectomy; the other 4 had delayed appendectomy six months after conservative therapy for appendiceal mass. All of the diagnoses were confirmed to be correct by pathologis examination . Among the other 89 children, the diagnosis was luteinic rupture in 4, choledochal cyst in 2, omental cyst in 1, hydronephrosis in 1, and nephrolithiasis in 1. Eighty of them were diagnosed as mesenteric lymphadenitis and treated conservatively. Seventy-six of these eighty children recovered , and appendectomy was performed on four patients. In two of them the diagnosis was suppurative appendicitis, and in two, the diagnosis was simple appendicitis. Conclusions Combined with consideration of the symptoms and signs, ultrasound is valuable in the diagnosis of appendicitis.