In comparisons of similar crashes between sexes, females exhibit an elevated risk of injury to the cervical spine and ribs. This preliminary study aims to investigate the relationship between upper body shape and shoulder belt fit, which may provide further insight into sex-based differences in seat belt loading and potential injury patterns. A non-ferromagnetic seat was fabricated for use with an open magnetic resonance (MR) imaging system, as well as a seat belt made of standard automotive webbing material with MR-visible markers. MR scans were acquired for 10 volunteers (5 female, 5 male) in an upright self-selected seat back position. This analysis focused on the shoulder belt positioning relative to the sternum and clavicle, with consideration of soft tissue interactions on this routing. Females in this study exhibited over three times greater range in the distance of the shoulder belt to the top of the sternum (SBD) compared to the males, despite similar or less variability than males in all gross anthropometric measures (SBD range, females:​ 21–116 mm, males:​ 51–78 mm). Such differences in variability highlight the diversity in routing patterns that may be influenced by different body geometries, such as breast tissue volume and distribution. Understanding how shoulder belt fit varies among and within diverse occupant populations highlights the need for improving the robustness of restraint design and performance.