BACKGROUND: Acute Appendicitis is the commonest acute abdominal condition requiring surgery worldwide.Over the years,high rate of negative appendicectomy with increased morbidity and mortality arising from diagnostic dilemma especially in atypical cases necessitated measures to improve diagnostic accuracy. One of such is development of clinical scoring system. AIMS: These were to determine the correlation of modified Alvarado score with histopathologic findings in acute appendicitis and the negative appendicectomy rate in National Hospital. METHODOLOGY: All the patients with clinical diagnosis of acute appendicitis who consented to the study were recruited by the researcher and modified Alvarado score was assigned to each before proceeding to surgery. RESULTS: Out of a patient load of 10,866 who were managed in surgical emergency/ outpatient department from June 2013 to June 2014 at National Hospital, Abuja,1,396 surgical operations were carried out, 143 (10.2%) of whom had appendicectomies after assigning MAS to each patient. Ninety-two out of the 131 patients analysed had histologic diagnosis of acute appendicitis resulting in negative appendicectomy rate of 29.8%, 41.3% in females and 14.3% in males.The MAS used in this study had 68.5% correlation with histopathologic finding in acute appendicitis, Sensitivity of 82% and Specificity of 68.5%. The Modified Alvarado Score variable with the highest sensitivity was tenderness at right iliac fossa(100%) while the lowest sensitivity was found in leukocytosis(25%). CONCLUSION: The Modified Alvarado score is a vital tool in improving the diagnostic accuracy as well as reducing negative appendicectomy rates especially in males. Additional investigations such as pelvic ultrasound scan or laparoscopy is recommended to improve the accuracy in females.