In Europe, emphasis is being transferred from injury prevention to accident prevention to reduce road casualties. This study attempted to identify the current potential for serious casualty reduction using passive safety by examining the crash performance of new cars with seriously injured occupants. The Co-operative Crash Injury Study conducts in-depth investigations of around 1200 vehicles per year from seven sample regions around England. Attention was focussed on passenger cars manufactured from 2004 to 2008 with at least one occupant injured to AIS level 3 or more. 28% of MAIS 3+ occupants were unbelted and 40% were belted but involved in crashes with limited potential for passive protection. A further 32% of occupants were belted and involved in crashes with potential for improved crashworthiness design. For these occupants, five major functional requirements were identified for crashworthiness improvement: a reduction of seatbelt loads on the chest and abdomen in frontal crashes, particularly for seniors; reduction in femur and tibia loads in frontal crashes; provision of head and chest protection in near-side crashes; and reduction of occupant lateral excursion in far-side impacts. Together these functions accounted for 70% of the identified requirements. Other smaller requirements were identified, each contributing up to 5% of total. Overall, the case supporting further developments in passive safety still appears significant.