It is recognized that utilizing 3D technology can provide greater insights into the dynamics of bone tissue. Past studies investigating the microstructure of cortical bone have predominantly used histology, a 2D form of analysis, to evaluate the age-related differences that occur within the histological structures of bone. Many of these studies have developed age-regression formulae to estimate age at death from the observed differences within the microstructure. The objective of this thesis was to integrate histology with high-resolution micro-CT to assess the age-related differences of cortical bone to produce an age-regression formula and evaluate the relation of the osteon geometry (circularity, aspect ratio, and osteon angle - theta) to osteon orientation (measured through phi). Upon investigation, it was determined that the reported precision (measured through Standard Error of the Estimate [SEE]) for age regression formulae is greatly affected by sample size, consequently, developing an age-estimation formula was not pursued due to the limited sample size available for this study. Therefore, the focus of this was to describe the age-related differences within 2D geometry of osteons and their relation to 3D osteon orientation (measured through phi). Twenty-seven, anterior, mid-femoral, female, specimens were analyzed. An unexpected negative correlation was found between osteon orientation (phi) to osteon circularity and aspect ratio, signifying that the orientation of osteons in 3D cannot be used to predict the geometry of osteons visualized in 2D. Nevertheless, these relations can likely be explained through the more dominant relations between osteon circularity and aspect ratio to age. My results demonstrate that osteons become more circular in their crosssections with advancing age independent of osteon orientation (phi). Interestingly, osteon orientation was also found to become oblique with age and not increasingly longitudinal as was expected. However, my results also suggest that osteons are being rotated two axes. As osteon orientation (phi) is rotated about the z-axis, my results indicate that the osteon angle (theta) is also being rotated about the x-axis. This was demonstrated through the negative correlation between osteon orientation (phi) and osteon angle (theta). This relation can potentially account for the negative correlation between osteon orientation (phi) and circularity since the appearance of increased circularity can be explained through the projection of the elliptical cross-section on to the imaging/sectioning plane. All together, my results establish that osteons are not cylindrical structures, especially in younger individuals, but are rather elliptical structures that become increasingly circular with advancing age.