A complete understanding of the anatomy, pathophysiology, and presenting signs and symptoms of appendicitis, combined with a thorough history and physical examination, will be the most important factors in allowing the practicing emergency physician to make the correct diagnosis of acute appendicitis. For patients in which the diagnosis is less clear or for patients in high-risk groups (extremes of age, pregnant women, and immunocompromised patients) additional diagnostic testing, usually US or CT, and early surgical consultation are recommended.