In both Germany and Denmark bills have been passed, that mopedists and motorcyclists should wear crash helmets in traffic. In an effort to elucidate the practical life-saving effect of such measures, this investigation has been performed in The Institute of Forensic Medicine, University of Aarhus, Denmark. Within the period 1959-1973 in all 188 mopedists killed in traffic accidents were submitted to medico-legal examination at the institute. All documents, including the police reports, photographs, the detailed autopsy-reports and medical case records were scrutinized in order to elucidate whether a crash helmet had been used during the accident, and if not, whether such use would have been life-saving. In 4 cases only, a crash helmet was used. Of the 188 moped drivers 54.2% died of scull-brain injuries, 33% of other injuries, while 12.8% died of combined scull-brain and other injuries. Following a thorough consideration of the circumstances and findings in each case, the authors in a retrospective judgment concluded, that 51% of the killed moped drivers probably should have survived the accident if they had worn an appropriate crash helmet. A further 8.5% might have survived. The authors admit that their material was selected and the results could hardly be considered indicative for the traffic in general, but are indicative of a tendency.