Appendicitis is one of the most common surgical emergencies. It remains a diagnostic challenge in patients who may present with atypical clinical complicating the diagnosis and leading to delay in the treatment, prolonged hospitalization, and unnecessary surgery. The advances in imaging techniques aid in the diagnosis of suspected acute appendicitis in an effort to avoid a negative appendectomy.　　Ultrasound and abdominal CT have a distinct advantage over clinical assessment alone in diagnosing appendicitis. The use of graded-compression US is found to be an accurate procedure that leads to a prompt diagnosis and early treatment of many cases of appendicitis. US is readily available, rapid, noninvasive, inexpensive, radiation free, dynamic, and a good screening test particularly in children, pregnant women, and centers with an established US program. However, it is highly operator dependent and has lower overall sensitivity and specificity than CT or MRI. CT is not widely available, is not operator dependent, and has excellent accuracy in the diagnosis of appendicitis. However, care must be taken to individualize the patients with an equivocal clinical presentation and to involve the surgical consultant early to yield the full benefits of CT scanning. There is still concern regarding radiation exposure in children and pregnant patients.　　The choice between the US and CT in the clinical setting is widely dependent on institutional preference, available expertise and experience, although patient age, sex, and body habitus are other important influencing factors. In conclusion, US should be an initial procedure for evaluation of patients suspected with acute appendicitis with CT as a complementary tool.