Introduction: Morphometric differences of several bones form the basis of sexual differentiation. The mastoid triangle has been widely used as a predictor of sexual differentiation. However, the radiographic measurements of the mastoid triangle, which form the clinical alternative of this parameter, have not been studied in the North Indian population. Therefore, we analyzed skull radiographs of live subjects to investigate the effectiveness of the radiographic mastoid triangle in sex determination.Methods: One hundred skull lateral radiographs (55 male and 45 female) from the digital archives of a tertiary care teaching institute in Northern India were retrospectively analyzed. The following parameters: porion-mastoidale length, mastoidale-asterion length, asterion-porion length, and area of the mastoid triangle were measured. Gender-based differences for these parameters were then calculated for any statistical significance. Further, the low value of Wilks' lambda, high values of Eigenvalues, and percentage of correct prediction accuracy denoted higher predictive value. Finally, discriminant function analysis was used to predict the relative validity of each measured parameter.Result: All measured parameters were significantly higher in the male group. The porion-mastoidale length was 32.21±2.15 mm in males and 31.66±3.21 mm in females. The mastoidale-asterion length was 50.00±9.75 mm in males and 49.84±6.97 in females. The asterion-porion length was 44.11±6.82 mm in males and 39.72±5.77 mm in females. The area of the mastoid triangle was 690.74±123.35 mm 2 in males and 570.57±130.0 mm 2 in females. The area of the mastoid triangle has the highest relative validity (78%). Conclusion:Considerable ethnic and racial differences have been observed in the radiographic morphology of the mastoid. The radiographic dimensions of the mastoid are potential predictors of sexual dimorphism. With the use of discriminant function analysis, the current study predicts the effectiveness of the area of the mastoid triangle as a reliable parameter for sexual differentiation in the Northern Indian population.