The purpose of this study was to assess, by use of computer simulations, the effectiveness of motorcycle helmets in reducing head and neck injuries in motorcyclist impacts. The computer model used was the MVMA Two-Dimensional Crash Victim Simulator. The study investigated a wide variety of impact conditions in order to establish a broad overall view of the effectiveness of helmets. It was found that helmet use invariably reduces dynamic responses which have a role in producing head injury and, in addition, almost always reduces the severity of neck response as well. For no configuration or condition does the helmet greatly increase the likelihood of neck injury. Thus, these simulations of a wide spectrum of motorcyclist impacts provide further evidence that helmet use significantly reduces the likelihood and severity of both head and neck injuries.This study was supported by the Insurance Institute for Highway Safety. Opinions, findings and conclusions expressed here are those of the authors and do not necessarily reflect the views of the Insurance Institute for Highway Safety.MOTORCYCLE CRASH INVESTIGATION data show that the use of helmets results in substantially fewer head injuries and fatalities (1). Few would disagree that helmets reduce the likelihood and severity of sharp and blunt trauma to the head resulting from head impacts. The effects on neck response of the addition of the helmet weight to that of the head, however, are not well understood.Many studies have indicated that the wearing of helmets does not increase the probability of sustaining neck injuries, but controversy on this point exists (2). It has been claimed that the mass of the helmet might cause increased loading of the neck structure during a crash event. Another view is simply that, apart from dynamic effects, if the head is protected, then greater energy must be absorbed by the neck. These views cannot be countered by epidemiological data at the present time because of both the difficulty in diagnosing neck injury in those cases where the cyclist survives and lack of well-defined neck autopsy protocol in those cases where the cyclist dies.In the past few years, some opponents of mandatory helmet laws have used unsubstantiated claims of the adverse role of helmets in neck injury causation as partial justification for having the laws repealed. In a review article, Versace (2) stated that “while the evidence does not support the theory that the helmet is a causal factor in the incidence of neck injury, the state-of-the-art does not provide sufficient data at this time which would indicate that the helmet does not increase the incidence of neck injury.” It was the intended purpose of the study discussed by this paper to expand the state-of-the-art so that this question and others pertaining to helmet use can be answered *1The research project described here had the following goals: 1) to address previously unanswered questions regarding neck response for helmeted and unhelmeted head impacts; 2) to model a range of cyclist impact situations accurately enough to provide useful quantitative measures of both head and neck responses; 3) to provide a basis for limited statements relating to helmet design; and finally, 4) to establish a broad overall view of the effectiveness of helmet use by investigating the potential of the helmet to both detrimentally and beneficially affect head and neck response.