There are numerous entities that can mimic acute appendicitis. Ultrasound and computed tomography are the most common first-line, cross-sectional imaging modalities in the acute care setting. Ideally, imaging will either confirm appendicitis or exclude it by identifying a normal appendix. In the latter scenario, an alternate diagnosis can frequently be established that range from genitourinary, gastrointestinal, to even abdominal wall processes. Imaging is especially helpful in cases of patients presenting with atypical signs/symptoms for acute appendicitis and those presenting with a classic presentation where an alternative diagnosis is determined. The correct diagnosis will allow the most appropriate clinical management and therapy; specifically, avoiding nonindicated surgery is essential. Common and uncommon mimics of acute appendicitis are discussed with specific attention to their sonographic and computed tomographic appearances.