Purpose: To analyse and interpret different sonographic findings in acute nonperforated and appendicitis.Materials and Methods: In 46 cases of acute appendicitis in children(26 girls, 20 boys) proven by surgery, sonographic findings were reviewed retrospectively. The findings of nonperforated and perforated appendicitis were analysed, focusing on the size, shape and echogenicity of the appendix, echo patterns of periappendiceal abscesses, mesenteric lymphadenopathy, and the prevalence of appendicolith. Results: A noncompressible distended appendix was present in 18 of 21 patients with nonperforated appendicitis and in 13 of 25 patients with perforation. In 18 patients with nonperforated appendicitis, the average diameter of distended appendix was 8.6mm;target appearance was noted in 16 patients and loss of echogenic submucosa in two. In 13 patients with perforated appendicitis, the average diameter of appendix was 9.1 mm;target appearance was noted in four patientsand loss of echogenic submucosa in nine. Periappendiceal abscesses were present in 21 of 25 cases of perforated appendicitis, and the echogenicity of abscesses was mixed in 12 patients, hypoechogenic in eight, and hyperechogenic in one. Mesenteric lymphadenopathy was present in two of 21 patients with nonperforated appendicitis and in four of 25 with perforation. Appendicolith was detected on sonography in three of 25 patients with perforated appendicitis, but was found in seven patients during surgery. One patients with perforated appendicitis also had right side hydronephrosis. Sonographically false-negative results were obtained in six cases. Conclusion : A sonographic examination was useful to differenciate perforated and nonperforated appendicitis in children. Loss of echogenic submucosa in the distended appendix and periappendiceal abscess formation were important findings in diagnosis of perforated appendicitis.