Acute appendicitis is the most common condition requiring emergent abdominal surgery in childhood. The clinical diagnosis of acute appendicitis is often not straightforward because approximately one-third of children with the condition have atypical clinical findings. The delayed diagnosis of this condition has serious consequences, including appendiceal perforation, abscess formation, peritonitis, sepsis, bowel obstruction, and death. Cross-sectional imaging with ultrasonography (US) and computed tomography (CT) have proved useful for the evaluation of suspected acute appendicitis. There has been a great deal of variability in the utilization of these modalities for such diagnosis in the pediatric population. The principal advantages of US are its lower cost, lack of ionizing radiation, and ability to assess vascularity through color Doppler techniques and to provide dynamic information through graded compression. The principal advantages of CT include less operator dependency than US, as reflected by a higher diagnostic accuracy, and enhanced delineation of disease extent in a perforated appendix.