This paper describes the injury relations which result when car-to-car crashes are analyzed using a computerized accident reconstruction procedure.The results of the study are presented in the form of graphical relations between injury severity and crash severity. Effects of factors such as impact location, seating position and vehicle weights are discussed. THIS PAPER EXPLORES the use of a relatively new tool for accident reconstruction - Simulation Model of Automobile Collisions (SMAC). The capability of this program to simulate a wide variety of crashes is described in detail elsewhere (1,2,3)*.This study is limited to the reconstruction of side impact collisions in which two passenger vehicles are involved. The need for redesigning vehicles based on an understanding of this crash condition is amply demonstrated by the fact that 28 percent of passenger car occupant fatalities and 41 percent of passenger car occupant injuries are caused by side impacts (4).The results obtained during this study are (a) the development of a methodology for data analysis and (b) a relation between crash severity and injury causation. The results are based on a small sample of cases from the Multidisciplinary Accident Investigation (MDAI) file and hence, definitive statistical conclusions are not possible. However, patterns are apparent and suggest relations between accident parameters and occupant injuries. These suggested relations are discussed and interpreted.The first section of the paper provides a brief description of the SMAC program and describes its use. This is followed by a discussion of the selection process for the cases which have been reconstructed. The final sections of the paper describe the reconstruction and the results.