The rear seat occupant has been the subject of an increasing number of research efforts in recent years. However, the majority of the research has focused on frontal impact, while there are also a number of studies concerned with low to moderate delta-V rear impact. Very limited work exists regarding the fate of the rear seat occupant involved in high-severity rear impact, especially when utilizing the BioRID anthropomorphic test device (ATD). Furthermore, it is evident that the out of position rear occupant, as defined by leaning forward prior to rear impact, is also of relevance to this line of research. The objective of this study is to explore and compare the response of BioRID and 50 th percentile Hybrid III in conjunction with the effects of head restraint geometry and the occupant seating configuration (normal seating versus forward leaning) in high-severity rear impact tests. Using a deceleration sled, BioRID and 50 th percentile Hybrid III were placed in the rear seat and subjected to a series of 22-mph delta-V rear impact tests. The pulse shape was representative of FMVSS 301 tests involving sedans. Six sled tests were conducted using two different head restraints and two ATD seating configurations. The ATD response data were analyzed with regard to three categories: 1) comparison of HIII and BioRID response, 2) influence of out-of-position seating configuration, and 3) effect of head restraint height. The data interpretation was augmented with motion tracking analysis to highlight potential kinematic root causes for the differences between HIII and BioRID response. It was found that the timing in impact response differed for both ATDs due to the structural disparity of their spines. Differences in time-histories of head acceleration, neck loads and moments were also discussed for the various testing configurations. It was also shown that HIII and BioRID produced contradictory neck data as a result of switching from a low profile to a high profile head restraint when tested in the leaning forward out-of-position setting.