The study of skeletal differences between males and females has rarely taken into account the physical change in hard tissue characteristics with the onset of advanced age. Anatomical change through degenerative modification may pose a challenge when diagnosing the sex of an unknown individual, especially if age is unknown. The aim of this study was to establish whether sexual dimorphism changes with age. This issue was addressed by using three types of procedural analyses. Firstly, standard measuring techniques were utilized to determine sex from 593 individuals. Visual (morphological) assessment was then performed on 608 individuals using sexually dimorphic traits in the distal humerus and pelvis. Lastly, over 300 individuals were analyzed with geometric morphometries using four locations on the postcranial skeleton. Younger females and males (50 years of age and younger) were then compared to older individuals (over 50 years of age) to determine if sexual dimorphism was increasing or decreasing with the onset of age. Long bone measurements of the postcranial skeleton increased with the onset of age in the most osteoporotic sample (South African white females). Males exhibited an increase in size, mainly in the knee and elbow joints, and black females remained static in their measurements with age. Older white females especially can sometimes incorrectly be misclassified as males. Visual techniques indicated that all populations have similar non-metric morphology in the distal humerus and pelvis. Classification accuracies in females decreased when viewing the distal humerus, indicating a decrease in sexual dimorphism at this location. Females appeared static in their pelvic morphology with the onset of age. Males remained sexually dimorphic throughout life in the humerus and pelvis. Geometric morphometries showed that the morphology of the distal humerus is sexually dimorphic, and does not change with age. Morphometries also confirmed the marked sexual dimorphism in the pelvis, and showed virtually no change in sexual dimorphism when comparing young to old groups.