It is the objective of this paper to emphasise the importance and benefit of the in-depth data analyses of injury mechanisms on bicyclists and motorcyclists. The in-depth investigations called “on scene in time” have been for the past 25 years carried out continuously at the Medical University of Hannover, under directives of the Federal Highway Research Institute (BASt). 1,000 accidents are reported every year on the basis of a statistical random spot-check plan. For this study 2,665 accidents with bicycles and 876 with so-called motorcycles and light motorcycles (80 cubic centimetres) during the years from 1985 to 1995 were analysed. Bicycles and motorcycles were compared in correlation and the collision and injury situation is described in detail. Conclusions are made for protective effect of helmets, serious scull-brain injuries and leg injuries.