In this study we compared the influence of cars' side deformations on injuries of near side belted front seat occupants in 27 real side collisions and 57 postmortal simulations. In the real accident group the deformation had a significant influence on the occurrence of lung contusions and pelvic fractures. There was a significant correlation between the number of rib fractures and deformation in the real accident group, and between rib fractures and deformation and age in the postmortal group. The minimum deformations in the real accident group (numbers in parentheses for the postmortal group) were for brain injuries 67 cm (33 cm), for lung contusions 50 cm (33 cm), for liver ruptures 45 cm (25 cm) and for pelvic fractures 40 cm (38 cm). The sometimes higher minimum values in the postmortal tests result from the direct exposition of the body to the impact. In the real accident group there were no survivors at a deformation > 50 cm. By means of logistic regression analysis it was possible to classify 85 % of the fatalities and 79 % of the survivors correctly. In both real accidents and postmortal tests the critical range for life threatening injuries was between 35 and 50 cm.