The sexual differences can be determined through morphological characteristics found in the ramus and body of mandible. The accuracy in determining sex is variable and the degree of sexual dimorphism in mandibles is different for each population. The aim of this study was to analyse nonmetric morphological characteristics of mandibles in adult Brazilian individuals, determining the anatomical variations found. In this study, 128 macerated mandibles of black and white Brazilian adults of both sexes were used. Of the 7 indicators analysed, the morphological characteristic that best distinguished the sexes was the shape of the chin, with an accuracy of 82.7% in black males, 61.9% in white males, 73.0% in black females and 75.0% in white females. The divergence of the gonial angle presented statistically significant differences between black males and black females, with an accuracy of 93.1% in black males and 34.3% in black females. An analysis of the shape of the chin is recommended as a reliable morphological indicator for the mandible in the diagnosis of sex from the skeletal remains of unknown individuals.