One of the most important paleodemographic and forensic determinations is age at death from the adult skeleton. Techniques now in use vary from direct observation of a bone to microscopic examination of a given segment. Yet since the 1920s, only a few parts of the skeleton have been focused upon for this assessment. It was not until the 1980s that a method from a new site, the sternal end of the rib, was introduced. The rib studies were based on a sample of recent medical examiner's cases including bones from over 300 American Whites and Blacks of both sexes. All specimens came from individuals of documented age, sex, and race. The ribs were first separated by sex and race then assigned to one of nine phases (0-8) based on the progression of changes observed at the costochondral junction. These included the formation of a pit, its depth and shape, configuration of the walls and rim surrounding it, and the overall texture and quality of the bone. Statistical analysis indicated that the morphological characteristics defining the phases were age related. There also were significant differences in the rate and pattern of metamorphosis by sex and race. The White male and female phase standards were blind tested and found to be easy to apply with little interobserver error between groups of judges divided by levels of education and experience. A comparison of age assessments from ribs and pubic symphyses from the same individuals revealed that twice as many ribs as symphyses were correctly phased. As with all skeletal methods there are some concerns with factors such as intraskeletal (in this case intercostal) variation, population specificity, and archaeological preservation. However, the rib phase technique can provide a more consistently accurate estimation of age within a narrower range than most other age assessment methods available today.