This study clearly shows that the sacrum can be used to make forensically significant estimates of age at death. The method uses seven developmental and degenerative traits that are assessed with presence-absence scoring. Scoring traits on a presence-absence basis rather than the assessment of multiple character states significantly increased the correlation of chronological assessments to age. By presenting both one and two standard deviation ranges of error, the method is useful in both bioarchaeological and forensic anthropological settings. This method is similar to other forensic-based age-estimation methods in that it is best suited for inclusion with multiple age marker methods and not as a stand-alone technique. The development of this new aging method involved a sample of 384 paired ilia and sacra from the Hamann-Todd collection, ranging in age from 10 to 96, together with 249 specimens from the W. M. Bass collection. The construction of the age-determination method involved multiple stages of trait identification, character-state definition, and age correlation; rank-order phase development; and percent-correct sample testing with phase and sample aggregation, all of which resulted in a six-phase component system for application to modern individuals. 8 figures, 3 tables, and 28 references