Pneumatization of the temporal bone is often included in descriptions of fossils and as a phylogenetic marker, but a number of questions about the evolution, growth, and development of the trait remain. Many studies have analyzed temporal bone pneumatization from a clinical perspective, but a systematic quantification of normal development of pneumatized spaces has not been conducted. In this study, ontogenetic change in the size and organization of temporal bone pneumatization is analyzed in a cross-sectional sample of humans. High resolution computed tomography scans of the temporal bone were acquired from a cross-sectional sample of humans (N = 28). Bone volume fractions, anisotropy, trabecular number, trabecular thickness, surface area, and volume were analyzed to provide information about the organization and size of pneumatized spaces across ontogeny. The results indicate that there are general and region-specific patterns of ontogenetic changes in the organization of pneumatized spaces. These changes reflect the transition from nonpneumatized bone to pneumatized bone. It also demonstrates that those regions that are pneumatized early in ontogeny (such as the mastoid antrum) continue to remodel after the initial period of pneumatization. The dynamic nature of temporal bone pneumatization over ontogeny suggests that this character requires careful consideration when used as a character for phylogenetic analyses. These results demonstrate the importance of comparing individuals from similar developmental stages, especially when completing quantitative analyses of the extent of pneumatization or organization of the spaces. Anat Rec,, 2011. © 2011 Wiley-Liss, Inc.