Biplane x-ray was used to image two cadavers in upright and inverted postures, and the three-dimensional variation in the relative abdominal organ position was quantified. The abdominal organs of each surrogate were instrumented with radiopaque markers using a minimally invasive approach. Imaging was performed with a known stomach volume, with residual air removed from the abdominal cavity, and with ventilation and perfusion. Marker positions were determined in two planar x-ray perspectives using target tracking software and projected into calibrated three-dimensional coordinates. Intuitive changes in organ position were observed with the effect of gravity in the upright orientation; in the superior-inferior direction, the separation between the most cranial and caudal diaphragm and liver markers was 95 mm to 169 mm. When inverted, the abdominal organs shifted cranially and fell within 66 to 81 mm in the superior-inferior direction. The relative change in position of the diaphragm markers, determined as the vector magnitude from the upright to the inverted position, was 99 to 121 mm. These data were scaled and compared to positional MRI data from nine human subjects in seated postures and the Global Human Body Models Consortium (GHBMC) model geometry. The overall shapes and relative positions of the inverted cadaver organs compared better to the human subjects and model geometry. These results give rise to several issues for consideration when interpreting cadaver test results and comparing them to finite element simulations and their associated injury prediction abilities.