This paper summarises a study designed to answer the following question: what are the benefits to Swedish society of road safety research in Sweden funded by the Swedish Transport Research Council and the programme for vehicle safety research during the period 1971-2004? The paper starts by discussing whether research can answer this question at all and explains why a well-controlled study was not feasible. A case study approach was selected, and five major research projects were examined in detail for the purpose of trying to estimate their effects on road safety. Estimates of safety effects were developed for four of the projects, indicating that road safety measures that were at least to some extent based on the findings of the research projects have made major contributions to reducing the number of road accident fatalities in Sweden. The estimates are not analytically rigorous and should be treated as qualified guesses only. Causal inferences are not possible. Nevertheless, if taken at face value, they show that the benefits to society of road safety research are large and outweigh by a wide margin the costs of the research, and of the road safety measures developed as a result of research. Thus, even if the estimated safety benefits exaggerate the true effects, the benefits of applied road safety research are likely to be greater than the costs of conducting this research and implementing road safety measures developed by research.