Estimation of sex is the first step in the evaluation of unknown human remains.  The study aimed to establish a reliable and accurate method for sex determination in Egyptian individuals through metric analysis of the mastoid triangle using three-dimensional reconstruction techniques of computed tomography images, drive a cutoff point that would be useful in the estimation of sex with the calculation of sensitivity and specificity of this cutoff point. In this retrospective observational analytical study, the sample was composed of 132 CT images of skull recruited from Mansoura University Hospital, Radiology Department. The three limbs and angles of the mastoid triangle (formed by asterion, porion and mastoid apex) were measured on both sides. The area of the triangle was calculated by Heron's formula on the right side and left side individually then the sum of them was considered as the total area. Statistical analysis showed a significant difference between both sexes in the triangle limbs, area and the porion-mastoid apex- asterion angle. The receiver operating characteristic (ROC) curve analysis was performed and the best variable was the total area providing 69% accuracy. Univariate discriminant analysis showed cross-validated classification accuracies 69.3%, 80.3% and 75% for males, females, and combined respectively. The multivariate discriminant analysis demonstrated reduced classification percentages.  Based on the results, a reference table was developed to be applied for the sex estimation of Egyptian individuals. In conclusion, the mastoid area is sexually dimorphic in Egyptian skulls and can be used as a relatively good sex discriminator.