Tehran University of Medical Sciences Frontiers in Emergency Medicine 2717-3593 3 2 2019 02 20 e20 e20 Nadien Fahim Faculty of Clinical Pharmacy, Zagazig University, Zagazig, El-Sharkia, Egypt Ahmed Negida Faculty of Medicine, Zagazig University, Zagazig, El-Sharkia Ahmed Fahim Ophthalmology Department, Nasser Institute Hospital, Cairo, Egypt 2019 02 16 2019 02 20 In the previous educational articles, we explained how to calculate the sample size for a rate or a single proportion and how to calculate the sample size for an independent cohort study. In this article, we will explain how to calculate the sample size for an independent case-control study based on the odds ratios or two proportions representing the exposure rates in the case and the control groups. https://fem.tums.ac.ir/index.php/fem/article/view/138 https://fem.tums.ac.ir/index.php/fem/article/download/138/103