This article forms part of an ongoing series of investigations designed to apply three-dimensional (3D) technology to problems in forensic anthropology. We report here on new morphometric data examining sexual dimorphism and population variation in the adult human mandible. The material is sourced from dissection hall subjects of South African and American origin consequently the sex and a statement of age are known for each individual. Thirty-eight bilateral 3D landmarks were designed and acquired using a Microscribe G2X portable digitizer. The shape analysis software morphologika (www.york.ac.uk/res/fme) is used to analyze the 3D coordinates of the landmarks. A selection of multivariate statistics is applied to visualize the pattern, and assess the significance of, shape variation between the sexes and populations. The determination of sex and identification of population affinity are two important aspects of forensic investigation. Our results indicate that the adult mandible can be used to identify both sex and population affinity with increased sensitivity and objectivity compared to standard analytical techniques.