Background: Acute appendicitis is one of the main pathological conditions requiring emergency surgical intervention. Many scoring methods have been applied to decrease the number of negative appendectomies. The aim of our study was to validate the efficiency of Alvarado scoring system in diagnosis of acute appendicitis. Methods: A prospective study was conducted on group of patients clinically diagnosed as acute appendicitis at Ain Shams University Hospital and was carried out on 150 patients in the period from March 2017 to February 2018. Data were collected and analyzed by the computer using IBM SPSS software package. Results: Our study included 92 male patients (61.3%) and 58 female patients (38, 6%) with (male: female) rate of (1.56: 1). Their mean age was (21.2 ± 8.4), ranging from 9-43 with a median of 19. All patients were carefully examined; rebound tenderness was noted in 99 patients (66%). Modified Alvarado score was calculated for each patient. In our study, we set a cut off value of MAS ≥ 7 and the overall specificity of the test at the score 7 was 52.94% (62.5% for males and 44.44% for females). Conclusion: The Alvarado score is a reliable, cheap, and reproducible diagnostic method which can be used by the primary care physician and the emergency room physician to evaluate a patient who presents with pain in the right lower abdominal quadrant. Keywords: Appendicitis, appendectomy, Alvarado, scoring system.