Efforts to reduce the toll of bicycle-related head injuries illustrate how the basic public health principles of surveillance, epidemiologic study, intervention, and evaluation can have a substantial impact on an injury problem, using a variety of injury-prevention strategies. Head injuries are the leading cause of serious morbidity and mortality from bicycle crashes. Helmets have been shown to reduce bicycle-related head injuries for cyclists of all ages involved in all types of crashes including those with motor vehicles. Helmet use has been promoted using educational campaigns, helmet subsidies, and legislation. Careful evaluation of these strategies has shown that these interventions increase helmet use and decrease the incidence of bicycle injuries. The model developed for the prevention of bicycle injuries is widely applicable to other injury problems.