The study validated the a priori assumption that midthoracic ribs are acceptable for age estimation if the sixth rib is unidentifiable or unavailable. It also shows the importance of evaluating multiple cross-sections in order to estimate adult age at death, because of the normal remodeling variation within individuals. The findings show that nonsixth ribs can provide similar osteon population density (OPD) values compared with those of the sixth ribs; however, the large variation in some of the OPD values of the same person indicates that remodeling may be occurring at different rates among ribs of the same person. Significant sampling error can occur within and between cross-sections, with the latter's sampling error increasing significantly as the amount of cortical area evaluated decreases. Frost recommends that a minimum of 50 square millimeters of cross-sectional bone in nonpathological individuals should be analyzed in order to minimize sampling error. Stout recommends the evaluation of two rib cross-sections for each individual. The study sample consisted of 120 cortical bone cross-sections from the middle third of ribs 3 through 8, which were removed from 20 cadavers. For each rib, OPDs and associated age estimates were calculated. 4 tables, 5 figures, and 37 references