**Abstract**

Acute appendicitis (AA) is a common surgical diagnosis in patients presenting to the Emergency Department with acute abdominal pain. A wide variety of other clinical conditions can present with a very similar presentation to acute appendicitis and therefore it can be occasionally challenging to make the correct diagnosis. In this review paper, the focus is to shed some light on the differential diagnosis of acute appendicitis which includes a variety of gastrointestinal, vascular, urological, and gynaecological conditions. In the emergency setting there are three main imaging modalities to evaluate patients presenting with abdominal pain, this includes computed tomography (CT), ultrasound (US) and magnetic resonance imaging (MRI). The choice of imaging modality for each clinical condition is variable and as such being familiar with those differential diagnoses is vital in deciding what is the best imaging modality for every patient presenting with abdominal pain.

**Keywords:** acute appendicitis, appendicitis mimics, emergency department, Alvarado score, aortic abdominal aneurysm, inflammatory bowel disease, infectious enterocolitis, diverticulitis, radiation enteritis, neutropenic colitis, Meckel's diverticulitis, mesenteric ischemia, urolithiasis, pyelonephritis, ectopic pregnancy, ovarian torsion, haemorrhagic ovarian cyst, pelvic inflammatory disease, Mittelschmerz
