This study comprises a total of 159 victims from bicycle accidents treated as inpatients at the Department of Neurosurgery, University of Bonn between January 1987 and June 1995. It was our aim to define the severity and features of bicycle-related head injuries in a defined population. Our results show that 33% of admitted bicycle victims sustained severe head injuries (Glasgow Coma Score 3-8). Neurosurgical operations were performed in 49% of patients and were mainly related to the evacuation of an extracerebral hematoma. Of the 159 bicycle victims, 112 (70%) made a good recovery, 11 (7%) remained moderately and 4 (3%) severely disabled, and 26 (16%) had died at follow-up (mean 2 years). In conclusion, our data indicate that bicycle-related trauma accounts for a substantial proportion of all head injuries requiring neurosurgical treatment. Active (e.g. traffic regulations, education of riders) and passive measures (e.g. safety helmets) can be expected to reduce both incidence and severity of head injuries among bicyclists.