Background: appendicitis is defined as an inflammation of the inner lining of the vermiform appendix that spreads to its other parts. Despite diagnostic and therapeutic advancement in medicine, appendicitis remains a clinical emergency and is one of the most common causes of acute abdominal pain and one of the most frequent surgical complains in the emergency room. Aim of the Work: the aim of this work was to compare the Appendicitis Inflammatory Response Score to the traditional Alvarado score to determine which is more accurate in the diagnosis of acute appendicitis. Patients and Methods: this descriptive prospective study was carried on 50 patients admitted to the surgical ER of Rashid General Hospital from December 2017 to April 2018 complaining from right lower quadrant pain between the age of 5 years old and 70 years old. All 50 patients had lower quadrant abdominal pain with suspicion of having acute appendicitis, all of them were thoroughly examined and both Alvarado Score and Appendicitis Inflammatory Response Score were applied to all of them, patients with moderate to high probability of having appendicitis(Alvarado Score = 7 or higher, AIR = 8 or higher) underwent open appendectomy and then the resected appendices were sent for histopathology to confirm the diagnosis. Results: the total number of cases with confirmed diagnosis of acute appendicitis by means of post-operative histopathology in our study was 46 out of 50 patients, the AIR score had sensitivity of 95.65% while the Alvarado score had sensitivity of 91.3%. Conclusion: this study demonstrates that the Appendicitis Inflammatory Response Score (AIR) appears to be more accurate than the Alvarado score, easy-to-use and reliable when dealing with a case of right lower quadrant pain with the suspicion of acute appendicitis and can help reduce the negative appendectomy rate.