Aim: To find out how accurate the Alvarado and Tzanaki scoring systems are in diagnosing acute appendicitis taking histopathology as gold standard. Methods: A cross-sectional prospective study was conducted from August 2019 to July 2020 at Department of General Surgery, Pakistan Institute of Medical Sciences Islamabad. Sixty patients were included, all of whom had appendectomies after a clinical diagnosis of acute appendicitis. Samples were submitted for histopathology, which was used as the gold standard for the definitive diagnosis of acute appendicitis. The specificity, sensitivity, positive predictive value (PPV), negative predictive value (NPV), diagnostic accuracy and negative appendectomy rate of Alvarado and Tzanaki scoring systems was calculated using SPSS version 23. Results: The sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of Alvarado score at optimal cut-off threshold of ≥7.0, were calculated as 74%, 55%, 90%, 27% and 71.66% respectively. The cut-off threshold point of Tzanaki score was set at more than 8, which yielded a 94.11% sensitivity and an 88.88% specificity. The positive predictive value was 99.95% and the negative predictive value was 72.72%. The Alvarado and Tzanaki scoring systems had negative appendectomy rates of 9.5% and 2.04%, respectively. Conclusion: The Tzanaki scoring system has a better diagnostic accuracy for acute appendicitis as compared to the Alvarado score. Keywords: Acute appendicitis, Alvarado score, Tzanaki score