This study aims at investigating head injury mechanisms for brain injuries, subdural or subarachnoidal haematoma (SDH or SAH) and skull fractures in adult pedestrian real world accidents by in-depth accident analysis and accident numerical reconstruction. Nine accident cases were carried out using a multi-body system pedestrian and cars' models to acquire the head impact conditions such as head impact velocity, position and orientation against the car's bonnet or windscreen. These impact conditions were then imposed on a head, car's windscreen and bonnet finite element model in order to calculate different mechanical parameters that are sustained by each victim during the impact. These calculated head stresses, strains and energies were then correlated with the observed injury patterns and compared to existing and available head injury mechanisms and tolerance limits. The accident investigation reports and pedestrian kinematics before the head impact came from the University of Birmingham (United Kingdom), INSIA (Spain) and DaimlerChrysler (Germany). They were worked out in the framework of an FP6 Integrated Project on Advanced Protection Systems (APROSYS). The head, the bonnet and the windscreen FEM, the injury mechanisms and tolerance limits have been developed at the University of Strasbourg (France) in a recent past. The reconstruction results show that the numerical tools employed predicted the observed injuries well. Nevertheless, it should be pointed out that the numerical tools used can only predict injuries reliably if both the pedestrian and vehicle side are modelled appropriately, i.e. with detailed finite element structures with well validated material and contact stiffness data. Brain neurological injuries were well correlated with brain Von Mises stress. Brain contusions occurred through high brain pressures. Skull fractures and SDH or SAH were well correlated with the global strain energy of the skull and of the brain/skull interface respectively. It has been concluded that these results showed that such numerical models are good tools to predict human head injuries. They will therefore be useful to improve the head protection devices i.e. the design, the conception, the evaluation and the optimization of cars' windscreens and bonnets against well defined injury criteria.