Introduction: Currently, there is little in the literature regarding the ability of rear seatbacks to act as a protective barrier from cargo in frontal crashes. However, it has been shown that unrestrained rear passengers pose a danger to front seat occupants. The association of rear seatback failures and intrusions with mortality and serious injury were examined.Methods: The Seattle CIREN database for restrained, rear-seat passengers in front-end crashes with seatback failure or intrusion was searched. Injury patterns and crash characteristics, including the role of unrestrained cargo were examined. Next, the National Automotive Sampling System-Crashworthiness Data System (NASS-CDS) database was queried for restrained rear-seat passengers in front-end crashes with recorded seat failure or intrusion. Mortality, maximum Abbreviated Injury Scale (AIS) score and mean Injury Severity Scale (ISS) scores were compared with passengers who had no failure or intrusion. Linear regression was used to identify the differences between the groups. Logistic regression was used to estimate the mortality risk associated with seat failure.Results: There were four CIREN cases that met the criteria. In each case, the occupant suffered significant injury or death. All four of the seat failures were the result of unrestrained cargo striking the seatback. The CDS data revealed a statistically significantly increased mortality (OR = 18.9, 95% CI = 14.0-25.7) associated with seat failure. Both the maximum AIS and mean of the ISS scores were higher in the failure/intrusion group (p <0.0001).Conclusions: Rear seatback failure/intrusion is associated with increased mortality and injury. Case reports suggest unrestrained cargo plays a significant role in these injuries.